POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power semiconductor devices:
• Power Diode
• Types of power diodes
•Diode reverse recovery characteristics
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power Diode:
Power diodes play an important role in power electronics
circuits. They are mainly used as uncontrolled rectifiers to
convert single-phase or three-phase AC voltage to DC. Typical
types of semiconductor materials used to construct diodes are
silicon and germanium. Power diodes are usually constructed
using silicon because silicon diodes can operate at higher
current and at higher junction temperatures than germanium
diodes.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power Diode:
When the anode terminal is positive with respect to the cathode
terminal, the pn-junction becomes forward-biased and the diode
conducts current with a relatively low voltage drop
When the cathode terminal is positive with respect to the anode
terminal, the pn-junction becomes reverse-biased and the
current flow is blocked
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power Diode:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power Diode:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
The figure depicts the reverse recovery characteristic of
a power diode. Whenever the diode is switched off the
current decays from IF to zero and further continues in
reverse direction owing to the charges stored in the
space charge region and the semiconductor region. This
reverse current attains a peak IRR and again start
approaching zero value and finally the diode is off after
time trr.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
This time is defined as reverse recovery time and is
defined as time between the instant forward current
reaches zero and the instant the reverse current decays to
25% of IRR
After this time the diode is said to attain its reverse
blocking capability
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
ta → time when charge from depletion region is
removed
tb → time when charge from semiconductor
region is removed
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
The area bounded by the triangular region
in the above figure represents the total
charge stored or reverse recovery charge,
QR. Hence we can write
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
putting in eq.1 and combining with eq.2,
It is equation 3 and putting 3 in 1 then
From eq. 3 and 4 we can see that trr and IRR depends on
QR which in turn depends upon the initial forward
diode current IF.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
If a diode has S-factor equals to unity it is known as softrecovery diode and for S-factor less that unity it is known
as fast or snappy-recovery diodes. S-factor indirectly
indicates the voltage transient that occurs upon the turn
off of the diode. Low S-factor implies high transient over
voltage while high S-factor implies low oscillatory reverse
voltage.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Reverse Recovery Characteristics of Power Diode:
The total power loss during turn off is the product of diode
current and voltage during trr. Most of the power loss occurs
during tb. In a typical data sheet of power diodes the most
important parameters given are IF avg, IF RMS, VRRM, I2t rating,
junction temp TJ, trr, S-factor, IRR. Apart form these many other
parameters and graphs are also provided
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Schottky Diodes:
The Schottky diode is often used in integrated circuits for highspeed switching applications. An example of a high speed
switching application is a detector at microwave frequencies.
The Schottky diode has a voltage current characteristic similar
to that of a silicon pn-junction diode. The Schottky is a subgroup
of the TTL family and is designed to reduce the propagation
delay time of the standard TTL IC chips.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Schottky Diodes:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Schottky Diodes:
One of the main advantages of the Schottky barrier diode is
its low forward voltage drop compared with that of a silicon
diode. In the reverse direction, both the breakdown voltage
and the capacitance of a Schottky barrier diode behave very
much like those of a one-sided step junction.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Schottky Diodes:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Schottky Diodes:
Features: International standard package Very low VF Extremely
low switching losses Low IRM-values Epoxy meets UL 94V-0
Applications: Rectifiers in switch mode power supplies (SMPS)
Free wheeling diode in low voltage converters
Advantages: High reliability circuit operation Low voltage
peaks for reduced protection circuits Low noise switching Low
losses
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Type
General Purpose
Diodes
Fast Recovery
Diode
Schottky Diodes
Voltage ratings
(VRRM)
Current ratings (IF)
50-5000 V
1A to several
thousand Amps
50-3000 V
Upto 100V
1A to several
thousand Amps
1-300 A
Reverse recovery
time (trr)
Applications
~25µs
UPS, battery
chargers, welding, –
traction etc.
<5µs
SMPS,
Doping done
commutation
using platinum or
circuits, choppers,
gold
induction heating
~ns
Very high
frequency
switching power
supplies and
instrumentation
Remarks
Metalsemiconductor
junction, usually
Al-Si(n-type),
majority carrier
device, hence
very low
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power semiconductor devices:
• Power BJT
• Power BJT over drive factor and Problem
• Classification of Semiconductor Switching device
• Controlled characteristics and types of power electronic
converters
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power BJT:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power BJT:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power BJT:
In the ON state, the ideal operating point occurs when the
collector current IC is equal to VCC /RC and VCE is zero. This occurs
when the base current equals the saturation current or IB = IB(sat)
In the OFF state, or cutoff point, the ideal operating point
occurs when the collector current IC is zero and the collector–
emitter voltage VCE is equal to the supply voltage VCC. The actual
operating point, in the OFF state, occurs when the load line
intersects the base current (IB = 0).
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power BJT:
𝑃𝑇(𝐵𝐽𝑇) = 𝐼𝐵 𝑉𝐵𝐸 + 𝑉𝐶𝐸 𝐼𝐶
𝐼𝐵
𝑂𝐷𝐹 =
𝐼𝐵𝑆
𝐼𝐶𝑆
𝛽𝑓 =
𝐼𝐵
In the circuit VCEsat=1V, VBEsat=1.5V, β=8-40 VB=10V,
Find i) the value of RB with ODF 5
ii) Forced β
iii) Total power loss
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Power BJT:
𝐼𝐶 =
𝑉𝐶𝐶 −𝑉𝐶𝐸
=18.0909A
𝑅𝐶
𝐼𝐵𝑆
𝐼𝐶𝑠
=
= 2.261𝐴
𝛽
𝐼𝐵 = 5 × 𝐼𝐵𝑆 = 11.3068𝐴
𝑉𝐵
𝑅𝐵 =
= 0.8844Ω
𝐼𝐵
𝐼𝐶𝑠
𝛽𝑓 =
= 1.6
𝐼𝐵
𝑃𝑇 = 𝐼𝐶𝑠𝑎𝑡 𝑉𝐶𝐸𝑠𝑎𝑡 + 𝐼𝐵 𝑉𝐵𝐸𝑠𝑎𝑡 =35.0511W
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Classification of Semiconductor Switching device:
1.Uncontrolled turn on and Off [Diode]
2.Controlled turn on and Uncontrolled turn off [SCR]
3.Controlled turn on and off characteristics [BJT, MOSFET, GTO]
4.Continuous gate signal requirement [BJT, MOSFET]
5.Pulse Gate Requirement [SCR, GTO]
6.Bipolar Voltage-withstanding capability [SCR]
7.Unipolar Voltage-withstanding capability [BJT, MOSFET, GTO]
8.Bidirectional Current capability [TRIAC, RCT]
9.Unidirectional Current Capability [SCR, GTO, BJT, MOSFET, Diode]
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Classification of Semiconductor Switching device:
Turn On and Off
•Uncontrolled On and Off
•Controlled On and Uncontrolled Off
•Controlled On and Off Characteristics
Voltage Withstanding and Current Capability
•Bidirectional
•Unidirectional
Gate Signal: Pulse and Continuous
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Control characteristics of power devices:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Control characteristics of power devices:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Types of Power Electronics Circuit:
1.Diode Rectifiers
2.AC-DC Converters (Controlled Rectifiers)
3.AC-AC Converters (AC Voltage Controllers)
4.DC-DC Converters (DC Choppers)
5.DC-AC Converters (Inverters)
6.Static Switches
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Types of Power Electronics Circuit:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Types of Power Electronics Circuit:
AC-DC Converters
•A single-phase converter with two natural
commutated thyristor is shown
•Average value of the output voltage can be
controlled by varying the conduction time
of thyristors
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Types of Power Electronics Circuit:
AC-AC Converters
•Used to obtain variable
AC output voltage from a fixed
AC source
•a single-phase converter with
a TRIAC is shown below
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Types of Power Electronics Circuit:
DC-DC Converters
• is also known as Chopper or Switching Regulator
• The average output voltage is controlled by varying the
conduction of transistor, .
• If is the chopping period, then is called as the duty cycle of
chopper
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Types of Power Electronics Circuit:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Types of Power Electronics Circuit:
DC-AC Converters
•Is also known as Inverter
•If transistor and conduct for one-half period and conduct the
other half, the output voltage is of alternating form
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
• V-I characteristics of SCR
• Two-transistor analogy
• Gate-triggering circuit design
• Triggering methods of SCR
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
A V-I Characteristic of SCR (Silicon Controlled Rectifier) is the
voltage current characteristics. The current through the SCR
varies as the Anode to Cathode terminal voltage and Gate to
Cathode terminal voltage is varied. The graphical representation
of current through the SCR and voltage across the anode to
cathode terminal is known as V-I Characteristics of SCR.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
Anode and Cathode terminals A and K are connected to variable
voltage source E through Load and Gate terminal G is connected
to the source Es to provide positive gate current through G to K
when switch S is closed. Va and Ia represents the voltage across
the anode to cathode terminals and current through the SCR
A plot between Va and Ia is drawn by varying the source voltage E
and noting the corresponding current through SCR. This plot
gives the V-I characteristics of SCR
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
Various Modes in V-I Characteristics of SCR
An SCR has three basic mode of operation: Reverse Blocking
Mode, Forward Blocking Mode and Forward Conduction Mode
An SCR in reverse blocking mode behaves as if an open switch
Hence this mode is also known as OFF state of SCR, junction J1 and
J3 are reversed biased while the junction J2 is forward biased.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
Forward Blocking Mode
Forward Blocking Mode is that operational mode of SCR in which
it does not conduct even though it is forward biased. The term
forward biased SCR implies that its anode terminal is positive
with respect to cathode terminal with gate switch S open, the
junction J1 and J3 are forward biased but junction J2 is reverse
biased
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor characteristics, two transistor model :
Forward Blocking Mode
Even through the SCR is forward biased, it does not conduct in
forward blocking mode, junction J1 and J3 are forward biased and
J2 is reversed biased. Increase VAK to such an extent which leads
to breakdown of the reverse biased junction J2. Apply positive gate
pulse between gate and cathode terminal. When the forward
biasing voltage is increased then at some critical voltage VBO
This critical voltage is known as Forward Breakover Voltage.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Two Transistor Model of SCR or Thyristor:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Two Transistor Model of SCR or Thyristor:
IC is collector current, IE is emitter
current, ICBO is forward leakage
current, α is common base forward
current gain and relationship
between IC and IB
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Two Transistor Model of SCR or Thyristor:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
•Forward Voltage Triggering
•Gate Triggering
•dv/dt Triggering
•Temperature or Thermal Triggering
•Light Triggering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
•Forward Voltage Triggering
As soon as avalanche breakdown at junction J2 occurs, current
starts flowing from anode to cathode of SCR
The value of this anode current is only limited by the load
Thus SCR is now in its conduction mode in forward direction from
anode to cathode
This is forward triggering method of turning SCR ON
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
•Forward Voltage Triggering
Normally this method is not used to turn on SCR as it may
damage it, Generally the forward breakover voltage is less than
reverse breakdown voltage and hence reverse breakdown
voltage is considered as final voltage rating while designing
SCR. It must also be noted and bear in mind that, once
avalanche breakdown take place at junction J2, the blocking
capability of J2 is lost
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
• Gate Triggering This method in which positive gate current is
flown in forward biased SCR to make it ON
Gate triggering is in fact the most reliable,
simple and efficient way to turn on SCR
In this method, positive gate voltage between
gate and cathode terminals are applied in
forward biased SCR which establishes gate
current from gate terminal to cathode
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
• Gate Triggering
Holding current is defined as the minimum value of anode current
below which it must fall for turning OFF the SCR or Thyristor
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
• Gate Triggering
When the gate current Ig is zero, the forward breakover voltage is VBO
As gate current increases from zero to Ig1, the forward breakover
voltage reduces from VBO to V1
Similarly, its value reduces from V1 to V3 as the gate current increases
from Ig1 to Ig3
Latching current is defined as the minimum value of anode current
which must be attained during turn on process of SCR to main the
conduction even when gate current is removed
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
• dv/dt Triggering
dv/dt Triggering is the technique in which SCR is turned ON by
changing the forward bias voltage with respect to time
dv/dt itself means rate of change of voltage w.r.t time, J2 is
reversed biased in a forward blocking mode of SCR
A reversed biased junction may be treated as a capacitor due to
presence of space charges in the vicinity of reversed biased
junction
I = C(dV/dt)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
• dv/dt Triggering
Therefore if the rate of rise of forward voltage (dv/dt) is high, the
charging current I will also be high. This charging current acts like
gate current and turns ON the SCR or thyristor even though the
gate current is zero. If should be noted that, it is rate of rise of
voltage which is responsible for turning the SCR ON. It is
independent of magnitude of voltage. The voltage may be low,
but the rate of its rise should be high enough to turn SCR ON.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
Temperature Triggering
This increased leakage current will again increase the junction
temperature and hence will further increase the reverse leakage
current. Thus, this process is cumulative and will eventually lead
to vanishing of depletion region of reversed biased junction J2 at
some temperature. At this temperature, the SCR will get turn ON
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Triggering Methods of SCR :
Light Triggering
If the intensity of irradiated light is exceeds a certain value,
forward biased SCR is turned ON. Note there that, irradiated
light produces free charge carries which is just like in case of
gate current. There charge carries move near the reversed
biased junction J2 and reduces the forward breakover voltage
This is the reason, the SCR gets turned ON. The SCR which is
turned ON by using light is called Light Activated SCR or LASCR.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Gate-triggering circuit design :
• Gate signal has to be cut-off, once the SCR is turned ON
(otherwise there is a power loss in gate circuit)
• Gate signal should not be given, when the device is connected in
the reverse bias
• The duration of gate pulse should be such that device has to
reach its latching current
• This circuit should have sufficient power to drive the PSDs
• It is better (compulsory in most of the applications) to provide
an isolation between power circuit and triggering circuit
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection and dv/dt protection:
For satisfactory and reliable operation, the specified ratings of an
SCR should not be exceeded due to overload, voltage transients
and other abnormal conditions
If the ratings are exceeded, there is a chance of damage
permanently to the SCR
Due to the reverse recovery process during the turn OFF the SCR,
the voltage overshoots occur in the SCR
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Also, during turn ON, switching action produces over voltages
in the presence of inductance
In the event of a short circuit, a large current flows through
the SCR which is very larger than the rated current
Therefore, to avoid the undesirable effects on the SCR due to
these abnormal conditions, SCR must be provided with
suitable protection circuits
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Overvoltage
Over voltages are the greatest causes of failure of SCRs
These transient over voltages often lead to unscheduled turn
ON of the SCR
Also, may lead to the permanent destruction of the SCR if the
reverse transient voltage is more than the VBR across the SCR
There are several causes of appearing these over voltages like
commutation , chopping , lightening , etc.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Internal Overvoltage
Internal over voltages arise while the SCR is in operation. During
the turn OFF of an SCR, a reverse current continues to flow
through the SCR after the anode current decreased to zero to
sweep away the earlier stored charge
This reverse current decay at a faster rate at the end of reverse
recover interval due to the inductance of the circuit, this high
di/dt produces a high voltage
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
External Overvoltage
This voltage value may be much higher than the rated value of
the SCR and hence the SCR may be damaged
These voltages are arises from the supply source or load, If SCRs
are in blocking mode in a converter circuit which is supplied with
transformer, a small magnetizing current flow through the
primary of the transformer. If the primary side switch is suddenly
removed, a high voltage transient is produced in the secondary of
the transformer and hence it is applied across the SCR
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
External Overvoltage
If the switches are provided on DC side, a sudden operation of
these switches produces arc voltages. This also gives rise the over
voltage across the SCR, This voltage is several times that of the
break over voltage of the SCR, Lightning surges on the HVDC
systems to which SCR converters are connected causes a very
high magnitude of over voltages, If the SCR converter circuit is
connected to a high inductive load, the sudden interruption of
current generates a high voltage across the SCRs
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Protection against over voltages
To protect the SCR against the transient over voltages, a parallel
R-C snubber network is provided for each SCR in a converter
This snubber network protects the SCR against internal over
voltages that are caused during the reverse recovery process
After the SCR is turned OFF or commutated, the reverse recover
current is diverted to the snubber circuit which consists of energy
storing elements
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Protection against over voltages
The lightning and switching surges at the input side may damage
the converter or the transformer and the effect of these voltages
is minimized by using voltage clamping devices across the SCR
Therefore, voltage clamping devices like metal oxide varistors,
selenium thyrector diodes and avalanche diode suppressors are
most commonly employed
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Overcurrent
During the short circuit conditions, over current flows through the
SCR. These short circuits are either internal or external. The
internal short circuits are caused by the reasons like failure of SCRs
to block forward or reverse voltages, misalignment of firing pulses,
short circuit of converter output terminals due to fault in
connecting cables or the load, etc. The external short circuits are
caused by sustained overloads and short circuit in the load
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
In case of DC circuits, fault current is limited by the source
resistance. Therefore, the fault current is very large if the source
impedance is very low. The rapid rise of this current increase the
junction temperature and hence the SCR may get damaged,
Hence the fault must be cleared before occurrence of its first
peak in other words fault current must be interrupted before the
current zero position
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Protection against overcurrent
The SCRs can be protected against the over currents using
conventional over current protection devices like ordinary fuses
(HRC fuse, rewirable fuse, semiconductor fuse, etc,), contractors,
relays and circuit breakers. Generally for continuous overloads
and surge currents of long duration, a circuit breaker is
employed to protect the SCR due to its long tripping time, For an
effective tripping of the circuit breaker, tripping time must be
properly coordinated with SCR rating
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
di/dt Protection of SCR
The anode current starts flowing through the SCR when it is
turned ON by the application of gate signal. This anode current
takes some finite time to spread across the junctions of an SCR
For a good working of SCR, this current must spread uniformly
over the surface of the junction
If the rate of rise of anode current (di/dt) is high results a nonuniform spreading of current over the junction
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
di/dt Protection of SCR
Due to the high current density, this further leads to form local
hot spots near the gate-cathode junction. This effect may damage
the SCR due to overheating. Hence, during turn ON process of
SCR, the di/dt must be kept below the specified limits
To prevent the high rate of change of current, an inductor is
connected in series with thyristor, Typical SCR di/dt ratings are in
range between 20- 500 ampere per microseconds.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
dV/dt Protection of SCR
When the SCR is forward biased, junctions J1 and J3 forward
biased and junction J2 is reverse biased, This reverse biased
junction J2 exhibits the characteristics of a capacitor, therefore,
if the rate of forward voltage applied is very high across the SCR,
charging current flows through the junction J2 is high enough to
turn ON the SCR even without any gate signal
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
dv/dt Protection of SCR
This is called as dv/dt triggering of the SCR which is generally not
employed as it is false triggering process, Hence, the rate of rise
of anode to cathode voltage, dv/dt must be in specified limit to
protect the SCR against false triggering. This can be achieved by
using RC snubber network across the SCR
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
Working of Snubber Circuit
The protection against high voltage reverse recovery transients
and dv/dt is achieved by using an RC snubber circuit
This snubber circuit consists of a series combination of capacitor
and resistor which is connected across the SCR
This also consist an inductance in series with the SCR to prevent
the high di/dt , The resistance value is of few hundred ohms
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
When the switch closed, a sudden voltage appears across the SCR
which is bypassed to the RC network. This is because the
capacitor acts as a short circuit which reduces the voltage across
the SCR to zero
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
As the time increases, voltage across the capacitor builds up at
slow rate such that dv/dt across the capacitor is too small to turn
ON the SCR, Therefore, the dv/dt across the SCR and the capacitor
is less than the maximum dv/dt rating of the SCR
Normally, the capacitor is charged to a voltage equal the
maximum supply voltage which is the forward blocking voltage of
the SCR
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
di/dt protection, dv/dt protection:
If the SCR is turned ON, the capacitor starts discharging which
causes a high current to flow through the SCR
This produces a high di/dt that leads to damage the SCR, hence,
to limit the high di/dt and peak discharge current, a small
resistance is placed in series with the capacitor as shown in above
These snubber circuits can also be connected to any switching
circuit to limit the high surge or transient voltage
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems :
𝑉𝐶 = 𝑉𝑠 (1
Derive the expression for
−𝑡
−𝑒 𝜏 )
−𝑡
𝑑𝑣
𝐼𝐶 = 𝐶
= 𝑉𝑠 (1 − 𝑒 𝜏 )
𝑑𝑡
𝑑𝑣
for
𝑑𝑡
the circuit given
Apply KVL then take LT and solve
for i(t) by taking LIT for RC series
circuit RC circuit with switch is
ON, we get
𝑉𝑠 −𝑡
𝑖 𝑡 = 𝑒𝜏
𝑅
At t=Ƭ,
𝑑𝑣
𝑑𝑡
=
0.6321𝑉𝑠
𝑅𝐶
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems : The thyristor (ideal)has latching current of 300mA
Determine the minimum duration of gate pulse
necessary to ensure turn-on
−𝑡
𝑉𝑠
𝑖 𝑡 = (1 − 𝑒 𝜏 )
𝑅
WKT in RL circuit Ƭ=L/R
Where i(t)=300mA
Only unknown is t, solve we get t=3.0937mS
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems : The capacitance of reverse bias junction J2 is
20pF, the limiting value of charging current to
turn on the thyristor is 16mA, determine the
critical value of dv/dt
𝐼=
𝑑𝑣
𝐶
𝑑𝑡
= 16𝑚A
𝑑𝑣
= 800𝑉/𝑢𝑆
𝑑𝑡
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems : The gate cathode characteristics of SCR is straight
line with a slope of 120, trigger source voltage is
10V and power dissipation at gate circuit is 0.5W,
determine the gate-source resistance
Since the slope is 120, that is the ratio of voltage to current,
hence 𝑃𝑔 = 𝐼 2𝑔 × 120, solve for Ig=64.549mA
𝑉𝐺𝐺 − 𝑉𝐺𝑆
𝑅𝑔 =
= 34.92Ω
𝐼𝑔
𝑉𝐺𝑆 = 120𝐼𝑔 = 7.745𝑉
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems : The gate cathode characteristics of SCR is straight
line with a gradient of 15V/A, passing through
origin. The minimum current required to turn on
thyristor is 500mA, calculate gate-source
resistance, assume that power dissipation is 0.5W
Since the gradient is 15V/A, so that ratio of voltage to current at
500mA is 7.5V
𝑉𝐺𝐺 − 𝑉𝐺𝑆
𝑅𝑔 =
= 15Ω
𝐼𝑔
𝑉𝐺𝑆 = 7.5𝑉
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems : The gate cathode characteristics of SCR is straight
line 1 + 10𝐼𝑔 = 𝐸𝑔 with supply voltage 10V
calculate gate-source resistance, assume that
power dissipation is 5W
Since the power is 5 = 𝐸𝑔 𝐼𝑔 so substitute for Eg, will get +ve and
–ve Ig, take +ve Ig and solve
𝑉𝐺𝐺 − 𝑉𝐺𝑆
𝑅𝑔 =
= 3.659Ω
𝐼𝑔
𝑉𝐺𝑆 = 7.5887𝑉
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems : The inductance L is added in the SCR circuit as
𝑑𝑖
shown, if = 50𝐴/µ𝑠, find the minimum value
𝑑𝑡
of L in order to protect the SCR
𝑑𝑖
𝐿 = 500
𝑑𝑡
𝐿 > 10𝜇𝐻
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Consider Vs=200V, R=5Ω, load and the stray inductances are
negligible. The thyristor is operated at 2kHz, if the required
𝑑𝑣
= 100𝑉/µ𝑠,and the discharged current to be limited to 100A
𝑑𝑡
find i) values of Rs and Cs
ii) Snubber loss
iii) power
rating of snubber resistor
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
−𝑡
𝑉𝑠
𝑉𝑠
𝑖 𝑡 =
𝑒𝜏
𝑅𝑠 = = 2Ω
(𝑅 + 𝑅𝑠 )
𝐼
𝜏 = 𝑅 + 𝑅𝑠 𝐶𝑠 = 7𝐶𝑠
1
𝑉𝑇 = 𝑉𝑠 − 𝑖 𝑡 𝑅
𝑡=
= 0.5𝑚𝑠
2𝑘
Problems :
𝑉𝑇 = 𝑉𝑠 −
−𝑡
𝑉𝑠 𝑅𝑒 𝜏
𝑅 + 𝑅𝑠
𝑑𝑣 𝑉𝑇 (𝜏) − 𝑉𝑇 (0)
=
𝑑𝑡
𝜏
(1)
In the equation (1)substitute at t=Ƭ
and t=0, we get VT=147.4457V and
57.1428V
Take Ƭ=7Cs and we get Cs=129nF
1 2 Power is E/T or E*f, hence P=5.16W= power rating
𝐸 = 𝐶𝑉 of snubber
2
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Problems : SCR connected with RL load, latching current of
20mA and it is fired by the pulse width of 50µs.
Determine whether SCR triggers or not R=20Ω
L=0.5H and Vs=100V
−𝑡
𝑉𝑠
𝑖 𝑡 = (1 − 𝑒 𝜏 )
𝑅
Substitute the given data, we get i=10mA, which is not enough
to trigger SCR or finding t, if it is less than 50us, then also it will
not turn on
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
GTOs, TRIACs, RCTs, SITHs and LASCR
The gate current required to turn off the GTO is relatively high
For example, a GTO rated with 4000V and 3000A may need 750A gate current to switch it off. So the typical turn off gain of
GTO is low and is in the range of 4 to 5
Due to this large negative current, GTOs are used in low power
applications
On the other hand, during the conduction state GTO behaves
just like a thyristor with a small ON state voltage drop
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
GTOs, TRIACs, RCTs, SITHs and LASCR
The GTO has faster switching speed than the thyristor and has
higher voltage and current ratings than the power transistors
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
GTOs: Construction
Consider the above structure of GTO, which is almost similar to
the thyristor
It is also a four layer, three junction P-N-P-N device like a
standard thyristor
In this, the n+ layer at the cathode end is highly doped to
obtain high emitter efficiency
This result the breakdown voltage of the junction J3 is low
which is typically in the range of 20 to 40 volts
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
GTOs: Construction
The doping level of the p type gate is highly graded because the
doping level should be low to maintain high emitter efficiency,
whereas for having a good turn OFF properties, doping of this
region should be high. The junction between the P+ anode and
N base is called anode junction. A heavily doped P+ anode
region is required to obtain the higher efficiency anode junction
so that a good turn ON properties is achieved However, the turn
OFF capabilities are affected with such GTOs
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
GTOs:
V-I characteristics
During the turn ON, GTO
is similar to thyristor in
its operates. When the
anode is made positive
with respect to cathode,
the device operates in
forward blocking mode.
By the application of
positive gate signal
triggers the GTO into
conduction state
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
GTOs:
V-I characteristics
The GTO can be turned OFF by the application of reverse gate
current which can be either step or ramp drive. The GTO can be
turned OFF without reversing anode voltage
The dashed line in the figure shows I-V trajectory during the turn
OFF for an inductive load. It should be noted that during the
turn OFF, GTO can block a rated forward voltage only
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
GTOs:
V-I characteristics
To avoid dv/dt triggering and protect the device during turn OFF,
either a recommended value of resistance must be connected
between the gate and cathode or a small reverse bias voltage
(typically -2V) must be maintained on the gate terminal. This
prevents the gate cathode junction to become forward biased
and hence the GTO sustains during the turn OFF state. It is
observed that, during reverse biased condition, after a small
reverse voltage (20 to 30 V) GTO starts conducting in reverse
direction due to the anode short structure
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Gate Turn-Off Thyristor Applications
•AC drives
•DC drives or DC choppers
•AC stabilizing power supplies
•DC circuit breakers
•Induction heating
•And other low power applications
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
TRIACs
TRIAC is an abbreviation for a TRIode AC switch. TRI means that
the device consisting of three terminals and AC means that it
controls the AC power or it can conduct in both directions of
alternating current.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
TRIACs
The triac has three terminals namely Main Terminal 1(MT1),
Main Terminal 2 (MT2) and Gate (G) as shown in figure. If MT1 is
forward biased with respect to MT2, then the current flows
from MT1 to MT2. Similarly, if the MT2 is forward biased with
respect to MT1, then the current flows from MT2 to MT1.
The terminal MT1 is connected to both N2 and P2 regions, while
MT2 is connected to both N3 and P1 regions.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Construction of TRIAC
Hence, the terminals MT1 and MT2
connected to both P and N regions
of the device and thus the polarity
of applied voltage between these
two terminals decides the current
flow through the layers of the
device
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Working and Operation of TRIAC
1.MT2 is positive with respect to MT1 with a gate polarity
positive with respect to MT1.
2.MT2 is positive with respect to MT1 with a gate polarity
negative with respect to MT1.
3.MT2 is negative with respect to MT1 with a gate polarity
negative with respect to MT1.
4.MT2 is negative with respect to MT1 with a gate polarity
positive with respect to MT1.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
V-I Characteristics of TRIAC
The traic function like a two
thyristors connected in antiparallel and hence the VI
characteristics of triac in the 1st
and 3rd quadrants will be
similar to the VI characteristics
of a thyristors
When the terminal MT2 is
positive with respect to MT1
terminal, the traic is said to be
in forward blocking mode
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
V-I Characteristics of TRIAC
Similarly, when the terminal MT2 is made negative with respect
to MT1, the traic is in reverse blocking mode. A small leakage
current flows through the device until it is triggered by breakover
voltage or gate triggering method. Hence the positive or negative
pulse to the gate triggers the triac in both directions.
The supply voltage at which the triac starts conducting depends
on the gate current. If the gate is current is being greater, lesser
will be the supply voltage at which the triac is turned ON
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Advantages and Disadvantages of TRIAC
• It can operate and switch both half cycles of an AC waveform
• The triac saves both space and cost in AC power applications
Disadvantages
• These
are available in lower ratings as compared with thyristors
• A careful consideration is required while selecting a gate trigger
circuit since a triac can be triggered in both forward and reverse
biased conditions
• These have low dv/dt rating as compared with thyristors
• These have very small switching frequencies(approx. 400Hz)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Applications of TRIAC
Due to the bidirectional control of AC, triacs are used as AC
power controllers, fan controllers, heater controllers, triggering
devices for SCRs, three position static switch, light dimmers, etc
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
RCTs, SITHs, LASCR, MOSFET and IGBT
The reverse conducting thyristor (RCT) is a thyristor associated
with an anti-parallel diode on a silicon crystal
The losses can be considerably reduced, the two components
are prevented from interfering with each other by means of
built-in protection rings
A simple method for assessing heat stress is described, as are
several applications (chopper, converter, electric filter) for
which this thyristor offers technical and cost advantages
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
RCTs, SITHs and LASCR
RCT (Reverse Conducting Thyristor)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
RCTs, SITHs and LASCR
RCT (Reverse Conducting Thyristor)
RCT monolithically integrated antiparallel diode on the
same silicon chip, This construction reduces to zero
the reverse blocking capability of RCT
A current pulse through the diode part of the chip
turns off RCT
The arrangement of ASCR and diode in a single device
reduces the heat sink size and leads to compactness of
the converter
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
RCT (Reverse Conducting Thyristor)
The undesirable stray loop inductance between ASCR and
diode is also eliminated and unwanted reverse voltage
transients across ASCR are avoided
This leads to better turn off behavior of RCT. It is with 2000 V
and 500 A ratings are available . For high performance inverter
and chopper circuits, RCTs can now be tailor-made
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
SITHs (Static induction Thyristor)
This is a device which is capable of
conducting large current with a low
forward voltage and it can turn-off
very fast, it is a self-controlled on-off
device
it is a high power, high-frequency
semiconductor device
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
SITHs (Static induction Thyristor)
FEATURES
• They are normally in on-state so gate electrodes will
be negatively biased to hold off-state
• At on-state it behaves similar to pin diodes
• It has the power handling capability similar to the GTO
• Faster switching speed than the GTO
• It is a level-triggered and voltage driven device
• In the si-thyristor the on-state voltage is low
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
SITHs (Static induction Thyristor)
ADVANTAGES
• It has high immunity for electromagnetic noise
• It can handle rapid voltage or current change
• It can obtain a higher breakdown voltage than FET(MOSFET)
• Low noise
• High audio frequency power capability
• It can be used in energy accelerator, current source inverter,
& high-frequency power conversion
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
LASCR (Light Activated SCR)
LASCR or light activated SCR is a semiconductor device which
turns ON when it is exposed to light
The constituent element of SCR is silicon, and it works like a
rectifier, and thus, it is termed as Silicon Controlled Rectifier
The LASCR is a type of thyristor which is triggered by photons
present in the light rays
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
LASCR (Light Activated SCR)
The gate terminal is used when the electrical triggering is
supplied to the LASCR, The advantage of using triggering of the
thyristor by light is prevention from electrical noise disturbances
It offers complete electrical isolation between the triggering
source and the switching device
The forward breakdown voltage decreases with increase in light
intensity, Thus, LASCR is considered to be one of the best devices
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
LASCR (Light Activated SCR)
The LASCR works on the principle of photoconduction that is
conduction due to photon striking the semiconductor surface
The LASCR is basically a thyristor, it is made up of
semiconductor material, the light rays falling on the device are
focused at one place to intensify it
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
LASCR (Light Activated SCR)
The more intensity of light, more will be the current through a
LASCR, The internal architecture of LASCR consists of two
transistors in such a way that the collector of one transistor is
connected to the base of another transistor
The light falling on the light activated SCR generates the
electron from the valence band, and these electrons will enter
conduction band. The electrons will move from collector of one
region to base of another region, and then the cascading effect
can be seen
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
LASCR (Light Activated SCR)
Applications of the LASCR
1.Low Power Applications: The Light activated SCR are generally
used for the application which requires low power to operate, This
is because power generated by SCR is low in magnitude
2.Motor Control: The LASCR finds applications in the working of
motor control
3.Computer Applications: The components used in the computer
system also require LASCR for meeting power requirements
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
LASCR (Light Activated SCR)
Applications of the LASCR
4. Optical light Controls: The optical light control use the principle
of photoconduction for generating the control signals
Therefore, the LASCR finds extensive application in optical light
control
5. Solid State Relay: In solid state relays, two LASCR are connected
in reverse parallel so that they can generate power in both the half
cycle of AC
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Enhancement MOSFET
Enhancement type MOSFET has no physical channel.
Enhancement type MOSFET can be either a n-channel or pchannel enhancement type MOSFET.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Enhancement MOSFET
The P-substrate extends up to the silicon dioxide layer. The two
highly doped n regions act as drain and source. When gate is
positive (VGS) free electrons are attracted from P-substrate and
they collect near the oxide layer. When gate to source voltage,
VGS becomes greater than or equal to a value called threshold
voltage (VT). Sufficient numbers of electrons are accumulated
to form a virtual n-channel and current flows from drain to
source.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
MOSFET Parameters
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
IGBT:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
IGBT:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
IGBT:
IGBT has three terminals gate (G), collector (C) and emitter (E).
With collector and gate voltage positive with respect to
emitter the device is in forward blocking mode. When gate to
emitter voltage becomes greater than the threshold voltage of
IGBT, a n- channel is formed in the P-region. Now device is in
forward conducting state. In this state p+ substrate injects
holes into the epitaxial n- layer. Increase in collector to emitter
voltage will result in increase of injected hole concentration
and finally a forward current is established
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
IGBT: Insulated Gate Bipolar Transistors) Features:
IGBT has high input impedance like MOSFET’s.
Low ON state conduction power losses like BJT’s.
There is no secondary breakdown problem like BJT’s.
By chip design and structure design, the equivalent drain to
source resistance RDS is controlled to behave like that of BJT.
Minority carrier devices, superior conduction characteristics, ease
of drive, wide SOA, peak current capability and ruggedness
Generally the switching speed of an IGBT is inferior to that of a
power MOSFET
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
Silicon-controlled rectifiers (SCRs)are now available with a voltage
rating up to 10 kV and a current rating up to 1200 A
In many power control applications, the required voltage and
current ratings are more than these maximum limits hence series
and parallel combinations are also often used when it is required
to control power in low-voltage high-current circuits or highvoltage low-current circuits because an SCR of suitable voltage
and current ratings may not be available
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
SCR are connected in series for high voltage demand and in
parallel for fulfilling high current demand
Sting efficiency can be defined as measure of the degree of
utilization on SCRs in a string
String efficiency < 1
Derating factor (DRF)= 1 – string efficiency
If DRF more then no. of SCRs will more, so string is more reliable
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
Two SCRs are have same forward blocking voltage, when system
voltage is more than the voltage rating of a single SCR
SCRs are connected in series in a string, there is a inherent
variation in characteristics
So voltage shared by each SCR may not be equal, For same
leakage current I0 in the series connected SCRs, For same
leakage current SCR1 supports a voltage V1 , SCR2 supports a
voltage V2
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
Σ𝑉
𝑆𝑡𝑟𝑖𝑛𝑔 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 𝜂 =
𝑛𝑉1
In steady state of operation , A uniform voltage distribution in the
state can be achieved by connect a suitable resistance across each
SCRs , so that parallel combination have same resistance
During steady state operation connect same value of shunt
resistance across each SCRs
This shunt resistance is called steady state equalizing circuit
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
Δ𝐼 = 𝐼1 − 𝐼2
𝐼2 = 𝐼1 − Δ𝐼
𝑉𝑠 = 𝑉𝐷1 + 𝑛 − 1 𝐼2 𝑅 = 𝑉𝐷1 + 𝑛 − 1 𝐼1 − Δ𝐼 𝑅
= 𝑉𝐷1 + 𝑛 − 1 𝐼1 𝑅- 𝑛 − 1 Δ𝐼 𝑅
𝑉𝐷1 =
𝑉𝑠 + 𝑛−1 𝑅Δ𝐼
𝑛
𝑛𝑉𝐷1 − 𝑉𝑆
𝑅=
(𝑛 − 1)Δ𝐼
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
𝑄 ∆𝑄
𝐶= =
𝑉 ∆𝑉
𝑉𝐷1
𝑉𝑠 + 𝑛 − 1 𝑅Δ𝐼
=
𝑛
Substitute in the VD1 equation and simplify
∆𝑄
𝑛𝑉𝐷1 − 𝑉𝑠 = (𝑛 − 1)
𝐶
(𝑛 − 1)∆𝑄
𝐶=
𝑛𝑉𝐷1 − 𝑉𝑠
∆𝑉
∆𝐼 =
𝑅
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
During turn ON and turn OFF capacitance of reverse biased
junction determine the voltage distribution across SCRs in a
series connected string
As reverse biased junction have different capacitance called
self capacitance, the voltage distribution during turn ON and
turn Off process would be different
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
Under transient condition equal voltage distribution can be
achieved by employing shunt capacitance as this shunt
capacitance has the effect of that the resultant of shunt and self
capacitance tend to be equal
The capacitor is used to limits the dv/dt across the SCR during
forward blocking state. When this SCR turned ON capacitor
discharges heavy current through the SCR
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Series and parallel operation of SCRs
The discharge current spike is limited by damping resistor R1
also damps out high frequency oscillation that may arise due to
series combination of C1 and series resistor
R1C1 are called dynamic equalizing circuit, During capacitor
discharge R1C1 comes into action for limiting current spike and
rate of change of current di/dt
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Parallel operation of SCRs
When current required by the load is more than the rated
current of single thyristor , SCRs are connected in parallel in a
string
• Here
should be a common heat sink,
making sure that the thyristors operate
at similar temperature.
• Current sharing should be equal. For
this resistors or inductors may be used in
series with the thyristors.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Parallel operation of SCRs
Static current sharing
Resistors are used in case of static current sharing. When
resistances are used in series, the losses may become high
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Parallel operation of SCRs
Dynamic current sharing
Inductors are also used in addition to the resistors. In case of
inductors (magnetically coupled), if current through the
thyristor T1 increases, an opposite polarity voltage would be
induced (as of series coil of T1) in the series coil of thyristor T2
The current flow is increased through the thyristor, serving the
purpose
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Ten thyristors are connected in a string to withstand DC voltage
Vs is 15KV. The max. leakage current and recovery charge
difference of thyristor are10mA and 150uC and each thyristor
has the voltage sharing resistor 56k and C=0.5uF, Determine
i) max. steady state voltage sharing
ii)Steady state DRF iii) Max.
transient voltage sharing iv) Transient state DRF
𝑉𝑠 + 𝑛 − 1 𝑅Δ𝐼
𝑉𝐷1 =
𝑉𝐷1 = 2.004𝑘𝑉
𝑛
𝑉𝑠
𝐷𝑅𝐹 = 1 − 𝜂 = 1 −
= 0.25149 𝑜𝑟 25.149%
𝑛𝑉𝐷1
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
iii) Max. transient voltage sharing
𝑉𝐷1
Δ𝑄
𝑉𝑠 + (𝑛 − 1) 𝐶
=
𝑛
𝑉𝐷1 = 1.77𝑘𝑉
iv) Transient state DRF
15000
𝐷𝑅𝐹 = 1 −
= 0.15254 𝑜𝑟 15.254%
10 × 1770
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Three phase converter is used for HVDC transmission system as
it operated from 25kV supply. The each thyristor of 1600 V/16A
are available. The forward leakage current difference is 35mA
The string efficiency is 85% and the change in charge is 25uC
Determine: i) No.of devices to be connected in series
ii) Values of equalizing components
𝑉𝑚𝑎𝑥 = 25𝑘𝑉 × 2
𝑉𝑠
𝑛=
𝜂𝑉𝐷1
𝑛 = 26
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
𝑛𝑉𝐷1 − 𝑉𝑆
𝑅=
(𝑛 − 1)Δ𝐼
(𝑛 − 1)∆𝑄
𝐶=
𝑛𝑉𝐷1 − 𝑉𝑠
𝑅 = 7.1867𝑘Ω
𝐶 = 0.1𝜇𝐹
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
SCRs with the rating of 1000V/200A are available to use in a string
to handle 6kV and 1kA. Calculate when DRF is i) 0.1 and ii) 0.2
When DRF is 0.1 is that efficiency is 90% that 𝑛 =
𝑉𝑠
𝜂𝑉𝐷1
= 6.666 = 7
When DRF is 0.2 is that efficiency is 80% that 𝑛 =
𝑉𝑠
𝜂𝑉𝐷1
=8
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
A string of four series connected thyristor is provided with static
and dynamic equalizing circuit. The string has to withstand an
off state voltage of 10kV, the static equalizing R=25k & dynamic
Rs=40Ω , Cs=0.08uF, the leakage current of four thyristors are
21mA, 25mA, 18mA & 16mA, Find
i) off state voltage across each SCR
ii) Discharge current of each capacitor at the time of turn ON
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
𝑉𝑠 = 𝑉𝐷1 + 𝑉𝐷2 + 𝑉𝐷3 + 𝑉𝐷4 = 10𝑘𝑉
𝑉𝐷1 = 𝐼 − ∆𝐼1 𝑅 Similarly write for other voltages and add then
10𝑘𝑉 = 25𝑘(4𝐼 − 80𝑚𝐴)
𝐼 = 0.12𝐴
𝑉𝐷1 = 2475𝑉, 𝑉𝐷2 = 2375𝑉, 𝑉𝐷3 = 2550𝑉 𝑎𝑛𝑑 𝑉𝐷4 = 2600𝑉
𝑓𝑜𝑟 𝑓𝑖𝑛𝑑𝑖𝑛𝑔 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑢𝑠𝑒 𝑅𝐶
𝑉𝐷1
𝐼1 =
= 61.875𝐴 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑙𝑦
40
𝐼2 = 59.375𝐴, 𝐼3 = 63.75𝐴 & 𝐼4 = 65𝐴
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Natural Commutation:
It is also called line commutation, the commutation is the process
Of turning off the thyristor, if the supply is AC, during reverse bias
SCR turns of by itself, which is known as natural/line commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
SCR turns off when
negative voltage appears
across the SCR. As there
are no special circuits
needed to turn off the
SCR
this
type
of
commutation is known
as natural commutation
It take place in Phase
controlled rectifiers, AC
voltage controllers and
Cyclo converters
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Forced Commutation
It is Applied to dc circuits
Forced Commutation is achieved by reverse biasing SCR device
or by reducing SCR current below the holding current value
Commutating elements such as inductance and capacitance
are used here
Forced commutation is applied to choppers and inverters
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Forced Commutation
Following are the methods used in forced commutation:
• Self commutation
• Impulse commutation
• Resonant pulse commutation
• Complementary commutation
• External pulse commutation
• Load Side Commutation
• Line Side Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Forced Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Forced Commutation
Applied to dc circuits, Commutation achieved by reverse biasing
the SCR or by reducing the SCR current below holding current
value, Commutating elements such as inductance and
capacitance are used for commutation purpose
Self-commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Forced Commutation
Self commutation
Self Commutation or Load Commutation or
Commutation (Commutation By Resonating the load)
Class
A
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Self commutation
Forced Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Self commutation
Forced Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Self commutation
Forced Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Forced Commutation
Problem on self commutation
In a self commutation circuit Vs=200V, L=5mH, C=20uF, find
the conduction time of thyristor, voltage across capacitor and
thyristor
𝑡𝑜𝑓𝑓 = 𝜋√𝐿𝐶=0.9929msec
𝑉𝐶 = 2𝑉𝑠 = 400𝑉
𝑉𝑇 = −200𝑉
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
‘C’ charged to a voltage VC (0) with polarity as shown
T1 is conducting and carries load current IL
To turn off T1 , T2 is fired
Capacitor voltage reverse biases T1 and turns it off
‘C’ Charges through load
T2 self commutates
To reverse capacitor voltage T3 is turned ON
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
T1 is turned off by applying a negative voltage across its
terminals, Hence this is voltage commutation
tC depends on load current, For higher load currents tC is
small, This is a disadvantage of this circuit
When T2 is fired, voltage across the load is V+VC hence the
current through load shoots up and then decays as the
capacitor starts charging
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
Problem
An impulse commutated thyristor circuit is shown in figure
Determine the available turn off time of the circuit if V = 100 V,
R = 10 Ω and C = 10 µF. Voltage across capacitor before T2is
fired is V volts with polarity as shown
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
Problem
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
Problem
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation) Problem
In the commutation circuit shown in figure C = 20 µF, the input
voltage V varies between 180 and 220 V and the load current
varies between 50 and 200 A
Determine the minimum and maximum values of available
turn off time tC
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Impulse Commutation (Class D Commutation)
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation
Initially C charged with polarity as shown in figure
T1 is conducting & IL is constant to turn off T1 , T2 is fired
iC(t) flows opposite to IL & T1 turns off at iC(t) = IL
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation with Accelerating Diode
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation with Accelerating Diode
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Resonant Pulse Commutation with Accelerating Diode
Diode D2 connected as shown to accelerate discharge
T2 turned on to turn off T1
Once T1 is off at t1 , flows through D2 until current reduces to iL
at time From t = t2 , ‘C’ charges through load, T2 self
commutates, But thyristor recovery process low hence longer
reverse bias time.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Problem
The circuit in figure shows a resonant pulse commutation
circuit. The initial capacitor voltage VC(0)=200V, C = 30µF and
L = 3µH. Determine the circuit turn off time tC , if the load
current IL is 200 A and 50 A
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Problem Repeat above problem For IL=200A if an antiparallel
diode is connected across thyristor1
(with accelerating Diode )
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Problem:
In a resonant commutation circuit supply voltage is 200 V.
Load current is 10 A and the device turn off time is 20µs. The
ratio of peak resonant current to load current is 1.5.
Determine the value of L and C of the commutation circuit.
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Solution:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques:
Complementary Commutation (Class C Commutation,
Parallel Capacitor Commutation)
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Two SCRs are used, turning ON one SCR turns off the other
T1 is fired, IL flows through R1
At same time ‘C’ charges towards ‘V’ through R2 with plate ‘b’
positive
To turn off T1 , T2 is fired resulting in capacitor voltage reverse
biasing T1 and turning it off
When T2 is fired current through load shoots up as voltage
across load is V+VC
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Problem
In the circuit shown in figure, the load resistances R1 = R2 = R = 5Ω
& the capacitance C = 7.5 µF, V = 100 volts. Determine the circuit
turn off time tC
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Problem:
Calculate the values of RL and C to be used for commutating the
main SCR in the circuit shown in figure. When it is conducting a
full load current of 25 A flows. The minimum time for which the
SCR has to be reverse biased for proper commutation is 40µsec.
Also find R1 , given that the auxiliary SCR will undergo natural
commutation when its forward current falls below the holding
current value of 2 mA
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Problem:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Solution:
In this circuit only the main SCR carries the load and the
auxiliary SCR is used to turn off the main SCR. Once the main
SCR turns off the current through the auxiliary SCR is the sum of
the capacitor charging current iC and the current i1 through R1 , iC
reduces to zero after a time tC and hence the auxiliary SCR turns
off automatically after a time tC , i1 should be less than the
holding current
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Solution:
POWER ELECTRONICS
Power devices and Thyristor commutation techniques
Thyristor commutation techniques: Complementary Commutation
Solution:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
Chopper is a static device, A variable dc voltage is obtained
from a constant dc voltage source
Also known as dc-to-dc converter, Widely used for motor
control, Also used in regenerative braking
Thyristor converter offers greater efficiency, faster response,
lower maintenance, smaller size and smooth control.
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
In step down chopper output voltage is less than input voltage.
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
When thyristor is
ON, supply voltage
appears across the
load
When thyristor is
OFF,
the
voltage
across the load will
be zero
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
METHODS OF CONTROL:
• Constant Frequency Control or Pulse width modulation control
• Variable Frequency control
Pulse Width Modulation
tON is varied keeping chopping frequency ‘f’ and chopping period
‘T’ constant
Output voltage is varied by varying the ON time tON
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
Pulse Width Modulation
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: Variable Frequency Control
Chopping frequency ‘f’ is varied
keeping
either
tON
or
tOFF
constant, to obtain full output
voltage range, frequency has to
be varied over a wide range
This
method
produces
harmonics in the output and
for large tOFF load current may
become discontinuous
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
A Chopper circuit is operating on TRC at a frequency of 2 kHz on
a 460 V supply. If the load voltage is 350 volts, calculate the
conduction period of the thyristor in each cycle
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
A transistor dc chopper circuit (Buck converter) is supplied with
power from an ideal battery of 100 V. The load voltage
waveform consists of rectangular pulses of duration 1 ms in an
overall cycle time of 2.5 ms. Calculate, for resistive load of 10 Ω.
(a) The duty cycle D. (b) The average value of the output voltage
Vdc. (c) The rms value of the output voltage Vrms. (d) The ripple
factor RF. (e) The output dc power.
Ans: a) 0.4 b) 40V c) 63.2V d) 1.225 e) 160W
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
A dc chopper has a resistive load of 20Ω and input voltage
VS=220V. When chopper is ON, its voltage drop is 1.5 volts and
chopping frequency is 10 kHz. If the duty cycle is 80%, determine
the average output voltage and the chopper on time.
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
In a dc chopper, the average load current is 30 Amps, chopping
frequency is 250 Hz. Supply voltage is 110 volts.
Calculate the ON and OFF periods of the chopper if the load
resistance is 2 ohms.
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
R = 10 and input voltage of V = 200 V. When chopper is ON, its
voltage drop is 2 V and the chopping frequency is 1 kHz. If the
duty cycle is 60%, determine
• Average output voltage • RMS value of output voltage
• Effective input resistance of chopper • Chopper efficiency
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E(motor) Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
When chopper is ON, supply is connected across load
Current flows from supply to load
When chopper is OFF, load current continues to flow in the same
direction through FWD due to energy stored in inductor ‘L’
Load current can be continuous or discontinuous depending on the
values of ‘L’ and duty cycle ‘d’
For a continuous current operation, load current varies between
two limits Imax and Imin
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
When current becomes equal to Imax the chopper is turned-off
and it is turned-on when current reduces to Imin
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
Expressions For Load Current iO For Continuous Current Operation
When Chopper Is ON (0 ≤ t ≤ tON)
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L Load:
When Chopper is OFF
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load(prolems):
A chopper is supplying an inductive load with a free-wheeling
diode. The load inductance is 5 H and resistance is 10Ω
The input voltage to the chopper is 200 volts and the chopper
is operating at a frequency of 1000 Hz. If the ON/OFF time
ratio is 2:3. Calculate:
• Maximum and minimum values of load current in one cycle
of chopper operation
• Average load current
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
A chopper feeding on RL load, With V = 200 V, R = 5Ω, L = 5 mH,
f = 1 kHz, d = 0.5 and E = 0 V
Calculate:
• Maximum and minimum values of load current
• Average value of load current
• RMS load current
• Effective input resistance as seen by source
• RMS chopper current
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
A 250 V dc motor fed by a chopper, runs at 1000 rpm with a duty
ratio of 0.8. What must be the ON time of the chopper if the
motor has to run at 800 rpm. The chopper operates at 100 Hz.
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
POWER ELECTRONICS
DC Choppers
Step-down Chopper With R-L-E Load:
An electric car has DC motor with chopper and the battery
voltage of 200V. It operates at a fixed frequency of 2kHz. The
motor resistance is 0.04 Ω and the total inductance of the circuit
is 0.1 mH. At the speed of 40 miles per hour, the motor develops
an induced emf of 60V. The chopper duty cycle while charging is
33.2%
Determine: i) peak-peak ripple current ii) DC component of
motor current iii) Avg. current of motor
Ans: 221.612A, 161.23A and 160A
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
An 80 V battery supplies RL load through a DC chopper. The load
has a freewheeling diode across it is composed of 0.4 H in series
with 5Ω resistor. Load current, due to improper selection of
frequency of chopping, varies widely between 9A and 10.2A
(a) Find the average load voltage, current and the duty cycle of
the chopper (b) What is the operating frequency f (c) Find the
ripple current to maximum current ratio
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
Input Current Is
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
Input Current Is
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
A DC Buck converter operates at frequency of 1 kHz from 100V
DC source supplying a 10 Ω resistive load. The inductive
component of the load is 50mH.
For output average voltage of 50V volts,
Find: (a) The duty cycle (b) ton (c) The rms value of the output
current (d) The average value of the output current (e) Imax and
Imin (f) The input power (g) The peak-to-peak ripple current.
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
POWER ELECTRONICS
DC Choppers
Step-down operation of chopper: with R-L load
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
In step up chopper output voltage is more than input voltage.
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
The values of L and C are chosen depending upon the
requirement of output voltage and current. When the chopper
is ON, the inductor L is connected across the supply. The
inductor current ‘I’ rises and the inductor stores energy during
the ON time of the chopper tON . When the chopper is off, the
inductor current I is forced to flow through the diode D and
load for a period, tOFF . The current tends to decrease resulting in
reversing the polarity of induced EMF in L
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
Diode D prevents any current flow from capacitor to the
source. Step up choppers are used for regenerative braking of
dc motors.
When Chopper is ON Voltage across inductor L =V, Therefore
energy stored in inductor = V I tON
When Chopper is OFF (energy is supplied by inductor to load)
Voltage across L is =VO- V
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
Neglecting losses, energy stored in inductor L = energy
supplied by inductor L
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
When the switch, the inductor, and the capacitor are treated as
ideal elements, or low-loss chopper circuit, the average power
dissipated by these components is zero. Consequently, the
average power supplied by the source must be approximately
equal to the average power delivered to the load.
That is,
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
Input to the step up chopper is 200 V. The output required is
600 V. If the conducting time of thyristor is 200 µsec.
Compute
•Chopping frequency,
•If the pulse width is halved for constant frequency of
operation, find the new output voltage.
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
A step up chopper has an input voltage of 150V. The voltage
output needed is 450V. Given, that the thyristor has a
conducting time of 150μseconds. Calculate the chopping
frequency.
The new voltage output, on condition that the operation is at
constant frequency after the halving the pulse width.
POWER ELECTRONICS
DC Choppers
Step-up operation of chopper:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
Switch Mode Power Supplies, or SMPS, are becoming
common place and have replaced in most cases the traditional
linear ac-to-dc power supplies as a way to cut power
consumption, reduce heat dissipation, as well as size and
weight. SMPS can now be found in most PC’s, power
amplifiers, TV’s, dc motor drives, etc., and just about anything
that requires a highly efficient supply as SMPS are increasingly
becoming a much more mature technology
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
The transformer is already a large component to have on a
printed circuit board (PCB)
Because of the constant power and heat dissipation, a linear
regulator power supply will require a heatsink
These two components alone add to a very heavy and bulky
device when compared to the small form factor of a switching
power supply
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
Preferred Applications:
• Electrolysis, waste treatment, or fuel cell applications
• DC motors, slot cars, aviation, and marine applications
• R&D, manufacturing, and testing equipment
• Battery charging for Lithium-Ion batteries used in aviation
and vehicles
• Electroplating, anodizing, and electroforming processes
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
Advantages
•Small form factor. The step-down transformer in an SMPS
operates at a high frequency which in turn reduces its volume and
weight
•High efficiency. Voltage regulation in a switching power supply is
made without dissipating excessive amounts of heat. SMPS
efficiency can be as high as 85%-90%.
•Flexible applications. Additional windings can be added to a
switching power supply to provide more than one output voltage
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
Disadvantages:
Complicated
design.
Compared
to
linear
regulators, planning and designing a switching power supply is
typically reserved for power specialists.
•High-frequency noise. The switching operation of the MOSFET
within a switching power supply provides high-frequency noise in
the output voltage. This often requires the use of RF shielding and
EMI filters in noise-sensitive devices.
•Higher cost. For lower power outputs of 10W or less, it’s cheaper
to use a linear regulated power supply
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
SMPS is a type of power supply that uses semiconductor
switching techniques, rather than standard linear methods to
provide the required output voltage
The basic switching converter consists of a power switching stage
and a control circuit
The power switching stage performs the power conversion from
the circuits input voltage, VIN to its output voltage, VOUT which
includes output filtering
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
The major advantage of the SMPS is its higher efficiency,
compared to standard linear regulators, and this is achieved by
internally switching a transistor (or power MOSFET) between its
“ON” state (saturated) and its “OFF” state (cut-off), both of
which produces lower power dissipation. This means that when
the switching transistor is fully “ON” and conducting current, the
voltage drop across it is at its minimal value, and when the
transistor is fully “OFF” there is no current flow through it. So
the transistor is acting like an ideal switch
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
Switch-mode power supplies (SMPS) are nonlinear and timevarying systems, and thus the design of a high-performance
control is usually a challenging issue. In fact, control should
ensure system stability in any operating condition and good
static and dynamic performances in terms of rejection of input
voltage disturbances and load changes
These characteristics, of course, should be maintained in spite of
large input voltage, output current, and even parameter
variations (robustness).
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
There are few points which are to be noted regarding SMPS
• SMPS circuit is operated by switching and hence the voltages
vary continuously
• The switching device is operated in saturation or cut off mode
• The output voltage is controlled by the switching time of
the feedback circuitry
• Switching time is adjusted by adjusting the duty cycle
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
The advantages of SMPS include,
• The efficiency is as high as 80 to 90%
• Less heat generation; less power wastage
• Reduced harmonic feedback into the supply mains
• The device is compact and small in size
• The manufacturing cost is reduced
• Provision for providing the required number of voltages
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
There are many applications of SMPS:
They are used in the motherboard of computers, mobile
phone chargers, HVDC measurements, battery chargers,
central power distribution, motor vehicles, consumer
electronics, laptops, security systems, space stations, etc
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
A switch mode power supply, can offer step-down, step-up and
negation of the input voltage using one or more of the three
basic switch mode circuit topologies: Buck, Boost and BuckBoost. This refers to how the transistor switch, inductor, and
smoothing capacitor are connected within the basic circuit.
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
The voltage drop across the inductor in mode 1 is
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
When the switch S is turned off, the current through the filter
inductor decreases and the current through the switch S is
zero. The voltage equation is
where iD is the current through the diode D
Due to high switching frequency
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
where Toff is the duration in which switch S remains off the diode
D conducts Neglecting the very small current in the capacitor Cf ,
it can be seen that io=isw for time duration in which switch S
conducts and io=iD for the time duration in which the diode D
conducts, The current ripple obtained
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
If the converter is assumed to be lossless, then
The switching period T can be expressed as
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
Using the Kirchhoff’s current law, the inductor current iL is
expressed as
If the ripple in load current ( io ) is assumed to be small and
negligible, then
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
The incremental voltage
across the capacitor ( Cf ) is
associated with incremental charge
by the relation
The area of each of the isosceles triangles
representing as
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
While the capacitor current is
positive,
the
capacitor
is
charging. From the definition of
capacitance,
POWER ELECTRONICS
DC Choppers
The Buck Converter with R Load and Filter:
The change in charge ∆Q is the
area of the triangle above the
time axis
POWER ELECTRONICS
DC Choppers
Buck converter operation:
A transistor dc chopper circuit (Buck converter) is supplied with
power form an ideal battery of 100 V. The load voltage waveform
consists of rectangular pulses of duration 1 ms in an overall cycle
time of 2.5 ms
Calculate, for resistive load of 10 Ω (a) The duty cycle γ
(b) The average value of the output voltage Vo (c) The rms value
of the output voltage Vorms (d) The ripple factor RF
(e) The output dc power
POWER ELECTRONICS
DC Choppers
Buck converter operation:
POWER ELECTRONICS
DC Choppers
Buck converter operation:
Buck regulator, Vs=50V, Vo=25V, peak-peak ripple current is
6.25A, fs=10kHz, determine i) duty ratio ii) value of inductance
iii) Value of capacitance to limit the ripple voltage 0.5V
i) D=0.5
𝑉𝑜 (1 − 𝐷)
𝐿=
∆𝐼𝑓𝑠
∆𝐼
𝐶=
8𝑓𝑠 ∆𝑉𝑐
ii) 200uH
iii) 156.25uF
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
The Boost Switching Regulator
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator
During the ON time the inductor current increases from its
minimum value toward its maximum value. In other words, the
stored energy in the inductor increases during the time the
switch is in the closed position
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
Boost converter operation:
The operation of the boost converter is relatively straightforward
When the switch is in the ON position, the inductor output is
connected to ground and the voltage Vin is placed across it
The inductor current increases at a rate equal to Vin/L
When the switch is placed in the OFF position, the voltage across
the inductor changes and is equal to Vout-Vin
Current that was flowing in the inductor decays at a rate equal to
(Vout-Vin)/L
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
It can be seen from the waveform diagrams that the input
current to the boost converter is higher than the output
current. Assuming lossless, boost converter, the power out
must equal the power in, Vin ⋅ Iin = Vout ⋅ Iout
From this it can be seen if the output voltage is higher than the
input voltage, then the input current must be higher than the
output current. In reality efficiency levels of around 85% and
more are achievable in most supplies
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
To obtain the input–output voltage relationship, apply the voltsecond balance rule to the inductor.
This implies that the area under the inductor voltage curve in
one period under steady state conditions should be zero
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
To obtain the input–output current relationship one can use the
100% efficiency constraint. This implies that
Inductor value:
The value of the inductor L is calculated on the basis of the amount
of current ripple that the designer would like to allow for a given
application.
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
Referring to the waveforms the slope of the inductor current
waveform during the period DTs is given as
Likewise the slope of the inductor current waveform during the
period (1 – D)Ts is given as
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
Here Vi and Vo are known from the converter specifications. D can
be obtained from the input-output relationship The switching
frequency fs is a design choice. From this Ts = 1/fs is obtained
ΔiL is also a design choice
The common choice in most cases is ΔiL = 10% of Iin. The output
power Po is known from the converter specifications. From the
knowledge of Po and Vo, Io is calculated Iin can be estimated for a
given load. The only unknown L can then be calculated
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
To regulate Vo with variations in Vi, the value of D should be varied.
Thus if Vimax is the maximum input voltage swing, then Dmin will be the
corresponding minimum duty cycle to obtain a specified Vo. If Vimin is
the minimum input voltage swing, then Dmax will be the corresponding
maximum duty cycle to obtain the specified Vo. Thus, for a regulated
Vo,
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
Here Vo, Vimax and Vimin are known from specifications of the
converter. Dmax is a design choice that is dependent on the specific
application
The inductor value should be calculated with the appropriate duty
ratio for a particular input voltage swing
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
Capacitor value:
It is calculated by applying the amp-second rule. Referring to the
capacitor current waveform, The area under the positive portion of
the current curve implies charging of the capacitor and that under
the negative portion implies discharging of the capacitor. For charge
balance both these areas should be equal. The change is the
capacitor charge ΔQ is given by the area under either the positive
portion or the negative portion of the capacitor current curve.
POWER ELECTRONICS
DC Choppers
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
Capacitor value:
In the case of the buck converter, the capacitor current is only the
inductor ripple current which is only a fraction of the load current
whereas in the case of the boost converter, the capacitor has to
handle a larger swing in the current through it Therefore, the
capacitor size is bigger in the case of the boost converter as
compared to the buck converter
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
With high chopping frequency and assuming linear and small
current variation, its solution is,
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
The average power supplied by the source must be
approximately equal to the average power delivered to the load
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
It is to be noted that the average current in the inductor for the
boost converter is not the same as the average load current,
which was true for the buck converter. The expressions for the
maximum and minimum currents through the inductor may now
be written as
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
The voltage regulation of practical chopper is very poor
A feedback regulator is therefore very essential for operation with
variable load to stabilize the output voltage
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
A boost converter is used to convert 12 V input to supply 50 W
at an output voltage of 48 V ± 0.5 %. The input current
variation shall be not more than ± 1%. If the switching
frequency is 10 kHz, specify the smallest inductance and
capacitance to meet the given specifications.
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
The step-up converter shown below is operated with a duty cycle
k = 0.75. The minimum value of the source current is I1 = 10 A
Assume that is decreases linearly when transistor Q is turned off.
Find the switching frequency of the converter.
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
The Buck-Boost Switching Regulator:
The DC output voltage value can be chosen to be higher or lower
than the input DC voltage.
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
The buck–boost converter has cyclic changes in topology due to
the switching action of the semiconductor devices. During a cycle
of operation, the main power switch is turned on and off, the
diode responds to this by switching off and on
Buck Boost Converter in mode 1
Buck Boost Converter in mode 2
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
Typical current waveforms in a buck–boost converter
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
Note that the inductor is transferring the energy it has obtained
from the source into the capacitor; the capacitor is being
charged up as the inductor is being discharged, and the output
voltage is rising
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
These four linear time-invariant differential equations describe
the state of the buck–boost converter
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
Current and voltage waveforms of Buck Boost Converter
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
1. The inductor current is continuous and this is made possible
by selecting an appropriate value of L
2. The inductor current in steady state rises from a value with
a positive slope to a maximum value during the ON state
and then drops back down to the initial value with a negative
slope Therefore the net change of the inductor current over
any one complete cycle is zero
POWER ELECTRONICS
DC Choppers
Buck-Boost Converter Continuous Mode of Operation
The relation of the voltage and current in mode 1 and mode 2 is given by
POWER ELECTRONICS
DC Choppers
Buck-Boost Converter Continuous Mode of Operation
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
A Buck-Boost converter is operating in dc steady state under the
following conditions
Assuming ideal components, calculate L
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator:
Consider the buck-boost converter with input voltage 14V, the
duty cycle is 0.6 and the switching frequency is 25kHz.
The L=180uH and C=220uF, the average load current I0=1.5A.
Calculate: a) Avg output voltage
b) peak-peak ripple voltage
c) peak-peak ripple current
d) peak current of device
Ans: -21V, 0.16V, 1.87A, (Is=2.25A) and 4.69A
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
The Buck Switching Regulator with boundary conditions:
The most common and probably the simplest power stage
topology is the buck power stage, sometimes called a stepdown power stage. Power supply designers choose the buck
power stage because the output voltage is always less than
the input voltage in the same polarity and is not isolated from
the input.
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
The Buck Switching Regulator with boundary conditions:
Inductor current waveform for the buck converter with different loads
POWER ELECTRONICS
DC Choppers
The Buck Switching Regulator with boundary conditions:
Further reduction in output load current puts the power stage
into discontinuous conduction mode
Discontinuous Current Mode
POWER ELECTRONICS
DC Choppers
Critical Condition at the Border of Continuous-Discontinuous Conduction:
At the Boundary I =Icritical Below we show the iL current waveform just
as it hits zero and tries to go negative.
The effective DC inductor
current is defined by the
three equivalent parameters:
ILB = IOB = IAV . Where the
subscript B refers to the
boundary of CCM to DCM
POWER ELECTRONICS
DC Choppers
Critical Condition at the Border of Continuous-Discontinuous Conduction:
The critical current for the buck converter is
Vo Constant
POWER ELECTRONICS
DC Choppers
The Buck Switching Regulator with boundary conditions:
Critical Inductance
A buck power stage can be designed to operate in continuous
mode for load currents above a certain level usually 5% to 10% of
full load. Usually, the input voltage range, the output voltage and
load current are defined by the power stage specification. This
leaves the inductor value as the design parameter to maintain
continuous conduction mode
The minimum value of inductor to maintain continuous
conduction mode can be determined by the following procedure
POWER ELECTRONICS
DC Choppers
The Buck Switching Regulator with boundary conditions:
Critical Inductance
The equation can be simplified and put in a form that is easier to
apply as
POWER ELECTRONICS
DC Choppers
The Buck Switching Regulator with Boundary Conditions:
In this Buck converter, the input voltage is varying in a range from
24V to 50 V. For each input value, the duty-ratio is adjusted to keep
the output voltage constant at its nominal value
(with Vin = 40 V and D = 0.3). Take switching frequency is 400kHz
Calculate the minimum value of the inductance L that will keep the
converter in the continuous conduction mode at Po = 5 W.
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator with Boundary Conditions:
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator with Boundary Conditions:
Example: For the 120 W boost converter, Vd (input) is crude DC
and varies from 12 to 36 V but D changes, via an undisclosed
feedback loop, to keep the output fixed at 48 V , Ts = 20usec
Io = 2.5 A,
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator with Boundary Conditions:
L < 18 uH guarantees always operate INSIDE the edge of the CCM to
DCM boundary on the DCM side.
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator with Boundary Conditions:
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator with Boundary Conditions:
POWER ELECTRONICS
DC Choppers
Switch mode regulators analysis and design:
Critical Condition at the Border of Continuous-Discontinuous Conduction:
The average inductor current is one-half the peak value:
A load resistance above this critical value results in less than a critical
load, causing the corresponding converter to go into DCM.
POWER ELECTRONICS
DC Choppers
The Boost Switching Regulator with Boundary Conditions:
Boost converter, the input voltage is varying in a range from 9V to
15 V. For each input value, the duty-ratio is adjusted to keep the
output voltage constant at its nominal value
(with Vin =12 V and D = 0.4). Take switching frequency is 400kHz
Calculate the critical value of the inductance L such that this Boost
converter remains in the continuous conduction mode at and above
Po = 5 W under all values of the input voltage Vin.
POWER ELECTRONICS
DC Choppers
The Buck-Boost Switching Regulator with Boundary Conditions:
Buck-Boost converter, the input voltage is varying in a range from
9Vto 15 V. For each input value, the duty-ratio is adjusted to keep
the output voltage constant at its nominal value (with Vin = 12 V
and D = 0.6). Take switching frequency is 400kHz
Calculate the critical value of the inductance L such that this BuckBoost converter remains in the continuous conduction mode at
and above Po = 5 W under all values of the input voltage Vin.
Ans: 16.75uH
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
MOSFET parasitic capacitance
Due to their structure, MOSFETs have a parasitic capacitance
The parasitic capacitance must be regarded as a parameter that
limits the usage frequency and switching speed
The gate-source capacitance Cgs and gate-drain capacitance Cgd are
the capacitance of the gate oxide film
The drain-source capacitance Cds is the junction capacitance of the
parasitic diode
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
MOSFET parasitic capacitance
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
MOSFET parasitic capacitance
The three parameters Ciss, Coss, Crss appearing on MOSFET data
sheets in general relate to these parasitic capacitances on data
sheets which provide separate descriptions of static
characteristics and dynamic characteristics, these are classified
as dynamic characteristics
These
are
performance
important
parameters
affecting
switching
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
MOSFET parasitic capacitance
Crss is the gate-drain capacitance Cgd itself and is called the
feedback capacitance or the reverse transfer capacitance,
This parameter greatly affects switching speed
These capacitances exhibit a dependence on the drain-source
voltage VDS
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
The resistive parameter is described as on-resistance, or RDS(ON) .
These conduction losses are inversely proportional to the size of
the MOSFET; the larger the switching transistor, the lower its
RDS(ON) and, therefore, its conduction loss.
The other source of power loss is through switching losses. As the
MOSFET switches on and off, its intrinsic parasitic capacitance
stores and then dissipates energy during each switching
transition.
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
The energy used to charge drain-source capacitance (also
referred to as output capacitance, Coss )
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
The losses are proportional to the switching frequency and the
values of the parasitic capacitances
The physical size of the MOSFET increases, its capacitance also
increases that increases switching loss
These sources of power loss create a significant challenge for
power supply designers, while a larger MOSFET will exhibit less
on-state resistance and consequently lower conduction loss, its
larger area drives up parasitic capacitance and switching loss
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
Drain source capacitance (Coss ) is present in all MOSFETs. In each
cycle, the energy stored in Coss is dissipated in the MOSFET, but
the amount of energy dissipated can vary widely depending
upon the MOSFET’s structure. Lateral MOSFETs exhibit Coss that
is significantly lower than that found in trench devices
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
if the output capacitance (Coss ) of the MOSFET in pF at an input
voltage of 400 VDC, it offers significantly lower power loss
(assuming parasitic winding capacitance (Cp) = 20 pF and
switching frequency (f) = 65 kHz).
Switching power loss for different MOSFET structures
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements: IGBT parasitic capacitance
IGBTs minority carrier devices, have superior conduction
characteristics, while sharing many of the appealing features of
power MOSFETs such as ease of drive, wide safe operating area
(SOA), peak current capability and ruggedness
The absence of the integral reverse diode gives the user the
flexibility of choosing an external fast recovery diode to match a
specific requirement
IGBT and a diode in the same package is available
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
Device capacitances (Cies, Coes, Cres)
The output capacitance has the typical voltage dependence of a
P-N junction
The reverse transfer (Miller) capacitance is also strongly
dependent on voltage
The input capacitance, which is the sum of the gate-to-emitter
and of the Miller capacitance
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
The diode co-packaged with the IGBT has much superior
switching characteristics than the integral body diode of high
voltage MOSFET and generates lower current spikes
This is a distinct advantage in those topologies that rely on an
anti-parallel diode
Smooth di/dt and dv/dt with minimal EMI signature and low
overshoots
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
The controlled current source is a function of the DC
characteristics of the IGBT, this current source is surrounded by
three capacitors and a resistor
The capacitor values of a real IGBT are dependent on the
collector emitter voltage and to cater for this dependence,
variable capacitors are used
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
Three deferent capacitors Cies, Coes and Cres could be distinguished
and measured, Cies is the input capacitance
The capacitance which is seen by shorting the collector to the
emitter and measure the capacitance between the gate and the
collector/emitter Cies = CGE + CCG
Coes = CCE + CCG , CGE = Cies – Cres , CCE = Coes – Cres , CCG = Cres
These three capacitances are all depending on the collector
emitter voltage VCE
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
As can be seen both Coes and
Cres are heavily dependent on
the voltage while Cies is almost
constant, Therefore, Cies is
approximated as a constant for
all voltages It is also clear that
the voltage dependency of Cres
and Coes is very nonlinear
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
For the very low voltage regions the capacitor values are in the
range of hundreds of nF, but very fast the capacitor values drop to
only a few nF, It is impossible this model exactly to these curves
and therefore this parameter often needs some tuning
One way to start is to take a certain capacitor and voltage value
somewhere in the middle of the curve
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
IGBT parasitic capacitance
The approximation of the deferent IGBT capacitors as a function
of the collector emitter voltage
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
Power supply designers choose the inverting buck-boost power
stage because the output voltage is inverted from the input
voltage, and the output voltage can be either higher or lower
than the input voltage
Inverting Buck-Boost Power Stage Schematic
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
The inverting buck-boost power stage with a drive circuit block
included. The power switch, Q1, is an n-channel MOSFET
The output diode is CR1. The inductor, L, and capacitor, C, form the
effective output filter
The capacitor ESR, RC, (equivalent series resistance) and the
inductor DC resistance, RL, are included in the analysis
The resistor, R, represents the load seen by the power stage output
POWER ELECTRONICS
DC Choppers
Non-ideal switches and parasitic elements:
Notice that in simplifying the above, TON + TOFF is assumed to be
equal to TS. This is true only for continuous conduction mode seen
in the discontinuous conduction mode analysis.
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Half Bridge Inverter:
The inverter is a power electronic converter that converts
direct power to alternating power. By using this inverter
device, we can convert fixed dc into variable ac power which as
a variable frequency and voltage. If the dc input is a voltage
source then the inverter is known as VSI (Voltage Source
Inverter). The inverters need four switching devices whereas
half-bridge inverter needs two switching devices.
POWER ELECTRONICS
Pulse-width-modulated inverters
Half Bridge Inverter:
Half-bridge inverter requires two diodes and two switches which
are
connected
in
anti-parallel.
The
two
switches
are
complementary switches which means when the first switch is
ON the second switch will be OFF Similarly, when the second
switch is ON the first switch will be OFF.
POWER ELECTRONICS
Pulse-width-modulated inverters
Single Phase Half Bridge Inverter with Resistive Load:
POWER ELECTRONICS
Pulse-width-modulated inverters
Single Phase Half Bridge Inverter with Resistive Load:
Where RL is the resistive load, Vs/2 is the voltage source, S1 and
S2 are the two switches, i0 is the current. Where each switch is
connected to diodes D1 and D2 parallel. In the above figure, the
switches S1 and S2 are the self-commutating switches. The switch
S1 will conduct when the voltage is positive and current is
negative, switch S2 will conduct when the voltage is negative, and
the current is negative. The diode D1 will conduct when the
voltage is positive and current is negative, diode D2 will conduct
when the voltage is negative, and the current is positive
POWER ELECTRONICS
Pulse-width-modulated inverters
Single Phase Half Bridge Inverter with Resistive Load:
Case 1 (when switch S1 is ON and S2 is OFF): When switch S1 is
ON from a time period of 0 to T/2, the diode D1 and D2 are in
reverse bias condition and S2 switch is OFF. Where output
voltage V0= Vs/2, Where output current i0 = V0/R= Vs/2R
Case 2 (when switch S2 is ON and S1 is OFF): When switch S2 is
ON from a time period of T/2 to T, the diode D1 and D2 are in
reverse bias condition and S1 switch is OFF. Where output
voltage V0= -Vs/2, Where output current i0 = V0/R= -Vs/2R
POWER ELECTRONICS
Pulse-width-modulated inverters
Single Phase Half Bridge Inverter with Resistive Load:
𝑉𝑜(𝑎𝑣𝑔) = 𝐼𝑜(𝑎𝑣𝑔) = 0
𝑉0(𝑟𝑚𝑠)
2
1 2𝜋 𝑉𝑠
= [ න
2𝜋 0
2
Fourier Series:
2
𝑉𝑠
𝑑 𝑤𝑡 ] =
2
POWER ELECTRONICS
Pulse-width-modulated inverters
Single Phase Half Bridge Inverter with Resistive Load:
Fourier Series:
As there is no DC offset so ao is zero and due to quarterwave symmetry, all the components in are an zero. So, the
contribution of bn will only remain & bn is given as
POWER ELECTRONICS
Pulse-width-modulated inverters
Single Phase Half Bridge Inverter with Resistive Load:
Fourier Series:
By putting the value of bn in Fourier series equation, we get
Vo = 0 for n=2,4,6,8…
ω is the angular frequency of the output voltage. The even
harmonics of the output voltage are not present due to
quarter-wave symmetry. Hence the result is
POWER ELECTRONICS
Pulse-width-modulated inverters
Single Phase Half Bridge Inverter with Resistive Load:
Fourier Series:
𝑉01 = 0.45𝑉𝑠
𝑉𝑜3
𝑉𝑜1
=
3
𝑉𝑜5
𝑉𝑜1
=
5
𝑉𝑜7
𝑉𝑜1
=
7
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Performance Parameters of Inverters:
Harmonic factor of nth harmonic, HFn
It is a measure of individual harmonic contribution. HFn versus the
control parameter gives the harmonic profile of the inverter. Small
HFn value is desired.
Harmonic factor of the nth harmonic (HFn)
Von
HFn 
Vo1
for n>1
Von = rms value of the nth harmonic component
V01 = rms value of the fundamental component
POWER ELECTRONICS
Pulse-width-modulated inverters
Performance Parameters of Inverters:
Total harmonic distortion, THD
It is a measure of closeness in shape between a waveform
and its fundamental component (sinusoidal waveform)
THD = 0 means sinusoidal wave

1
THD 
(  Von2 )
Vo1 n2,3,...
1
2
POWER ELECTRONICS
Pulse-width-modulated inverters
Performance Parameters of Inverters:
Distortion Factor, DF
DF indicates the amount of HD that remains in a particular
waveform after the harmonics of that waveform have been
subjected to the second order attenuation (i.e. divided by n2)
2


1
 Von  
DF 
   2  
Vo1  n  2,3,...  n  
DF of nth harmonic component, DFn
Von
DFn 
2
Vo1n
1
2
POWER ELECTRONICS
Pulse-width-modulated inverters
Performance Parameters of Inverters:
Lowest-order harmonic LOH
The harmonic component whose frequency is closest to the
fundamental, and its amplitude is greater than or equal to 3% of
the amplitude of the fundamental component.
POWER ELECTRONICS
Pulse-width-modulated inverters
Half Bridge Inverter: Problems
A single phase half bridge inverter has a resistive load of
R=2.4Ω and the DC input voltage is 48V, Find i) rms value of
output voltage at the fundamental frequency V01 ii) output
power iii) THD iv) DF v) The HF and DF of the LOH.
POWER ELECTRONICS
Pulse-width-modulated inverters
Half Bridge Inverter: Problems
POWER ELECTRONICS
Pulse-width-modulated inverters
Half Bridge Inverter: Problems
POWER ELECTRONICS
Pulse-width-modulated inverters
Half Bridge Inverter: Problems
The single phase half bridge inverter has a resistive load of 10Ω
and the center-tap dc input voltage is 96V, compute:
i) RMS value of the output voltage
ii) Fundamental component of output voltage
iii) First five harmonics of the output voltage
iv) Fundamental power consumed by the load
v) RMS power consumed by the load
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
•
•
•
•
Consists of 4 choppers and a 3-wire DC source
Q1-Q2 and Q3-Q4 switched on and off alternately
Need to isolate the gate signal for Q1 and Q3 (upper)
Each pair provide opposite polarity of Vsacross the load
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
Q1-Q2 on, Q3-Q4 off, Vo = Vs
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
Q3-Q4 on, Q1-Q2 off, Vo = -Vs
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A single phase bridge inverter has a resistive load of R=2.4Ω and
the DC input voltage is 48V, Find i) rms value of output voltage
at the fundamental frequency V01 ii) output power iii) THD iv)
DF v) The HF and DF of the LOH.
Ans: 43.2V, 960W, 48.34%, 3.8% and 3.704%
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A bridge inverter with RLC load R=10, L=31.5mH and C=112uF and
inverter frequency 60Hz Supply voltage Vs=220V(up to 9th
Harmonic)
i) Express the instantaneous load current in Fourier series ii) rms
load current at fundamental frequency iii) THD iv) power absorbed
by the load v) Average current of dc supply and vi) rms and peak
currents of each switch
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A 1Ø bridge inverter with RLC load R=4, L=35mH and C=155uF and inverter frequency
50Hz, supply voltage Vs=230V (up to 5th Harmonic)
i) Express the instantaneous load current in Fourier series ii) rms load current at
fundamental frequency iii) THD iv) power absorbed by the load at fundamental
frequency v) Average current of dc supply and vi) rms and peak currents of each switch
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A 1Ø bridge inverter with RLC load R=1, inductive reactance and
capacitive reactance are 6Ω and 7Ω respectively, supply voltage
Vs=230V, Find the power deliver to the load due to fundamental
component and phase angle difference
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
•
•
•
•
Consists of 4 choppers and a 3-wire DC source
Q1-Q2 and Q3-Q4 switched on and off alternately
Need to isolate the gate signal for Q1 and Q3 (upper)
Each pair provide opposite polarity of Vsacross the load
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
Q1-Q2 on, Q3-Q4 off, Vo = Vs
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
Q3-Q4 on, Q1-Q2 off, Vo = -Vs
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A single phase bridge inverter has a resistive load of R=2.4Ω and
the DC input voltage is 48V, Find i) rms value of output voltage
at the fundamental frequency V01 ii) output power iii) THD iv)
DF v) The HF and DF of the LOH.
Ans: 43.2V, 960W, 48.34%, 3.8% and 3.704%
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A bridge inverter with RLC load R=10, L=31.5mH and C=112uF and
inverter frequency 60Hz Supply voltage Vs=220V(up to 9th
Harmonic)
i) Express the instantaneous load current in Fourier series ii) rms
load current at fundamental frequency iii) THD iv) power absorbed
by the load v) Average current of dc supply and vi) rms and peak
currents of each switch
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A 1Ø bridge inverter with RLC load R=4, L=35mH and C=155uF and inverter frequency
50Hz, supply voltage Vs=230V (up to 5th Harmonic)
i) Express the instantaneous load current in Fourier series ii) rms load current at
fundamental frequency iii) THD iv) power absorbed by the load at fundamental
frequency v) Average current of dc supply and vi) rms and peak currents of each switch
POWER ELECTRONICS
Pulse-width-modulated inverters
Bridge Inverter:
A 1Ø bridge inverter with RLC load R=1, inductive reactance and
capacitive reactance are 6Ω and 7Ω respectively, supply voltage
Vs=230V, Find the power deliver to the load due to fundamental
component and phase angle difference
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter:
A 3 Phase Inverter converts the DC voltage into 3 Phase AC supply
Three Phase Inverter and its working, look at the voltage waveforms
of the three-phase line
In the above circuit, a three-phase line is connected to a resistive load
and the load draws power from the line
If we draw the voltage waveforms for each phase then a graph as
shown in the figure. In the graph, There three voltage waveforms
are out of phase with each other by 120°
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter:
There are two possible ways for triggering the switches to achieve the
desired result, one in which switches conduct for 180° and another in
which switches only conduct for 120°
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
During mode-1 for 0 ≤ ωt ≤ π/3 , transistor 1,5 and 6 conduct, During
mode-2 for π/3 ≤ ωt ≤ 2π/3 , transistor 1,2 and 6 conduct, During mode3 for 2π/3 ≤ ωt ≤ π , transistor 1, 3 and 2 conduct
Equivalent circuits for the three modes of operation for
180˚ conduction
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical
and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
For Y-connected load, the line to line voltage is √3 Vp
without delay angle, hence the three line-to-line
voltages are given by
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
Three phase inverter is fed from 500V DC source, it is
operated
with
180°
conduction
mode
which
is
connected to Y-connected R-load, Find i) Line rms &
Phase rms voltages
ii) Find fundamental line and phase
voltages
i) 408.25V & 235.5V ii) 389.8V & 225.05V
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 180° Conduction Mode:
Three phase inverter with 180° conduction R=5Ω,
L=23mH, inverter frequency is 60Hz, supply voltage is
220V, express instantaneous line voltage & line current
(up to 9th harmonics)
Also find line & phase rms voltages & at fundamental
frequency, THD and output power
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical
and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
The rms value of the output voltage waveform of 120˚
mode inverter shown for phase-a can be obtain as,
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
The line-to-line voltages for star-connected load can
be found as:
The line-to-neutral voltages shown can be expressed in
Fourier series as:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
The rms value of the fundamental component is
The rms value of the fundamental component is
The line-to-line voltage waveform is Vab = √3Van with
phase lead of 30˚ can be expressed in Fourier series
as:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
Formula of Phase and Line Voltage:
RMS Value of Phase Voltage = 0.4082Vs
RMS Value of Line Voltage = 0.7071Vs
RMS Value of fundamental phase voltage =
0.3898Vs
RMS value of fundamental line voltage = 0.6752Vs
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
The three-phase inverter in used to feed a Y-connected
resistive load with R =15 Ω per-phase. The d.c. input to the
inverter Vdc = 300 V and the output frequency is 50 Hz. If
the inverter is operating with 120˚ conduction mode,
calculate : (a) The peak and rms value of the load current
IL, (b) The output power, and the average and rms values of
the current of each transistor
POWER ELECTRONICS
Pulse-width-modulated inverters
Three Phase Inverter- 120° Conduction Mode:
The rms value of the thyristor current is
POWER ELECTRONICS
Pulse-width-modulated inverters
A three-phase transistor voltage-source inverter supplies
a three-phase load, The load consists of star connected
resistance of 10 Ω in each phase. The inverter supply
voltage is 200V d.c. and each inverter switch conducts for
120˚.
(a) Calculate the rms values of the first five harmonics in
the line- to-line output voltage, including the
fundamental.
(b) Calculate the rms values of the first five harmonics in
the line-to-neutral output voltage, including the
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical
and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
A more common method of controlling the voltage
within an inverter involves the use of pulse width
modulation (PWM) techniques. With this technique the
inverter output voltage is controlled by varying the
duration of the output voltage pulses
PWM is simply the variation (modulation) of the duty of
a square pulse to produce a controlled average voltage.
In its simple form, PWM is obtained by comparing a
reference signal, Ar (also called the modulating wave)
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
PWM technique: (a) low value of modulation index M, (b)
moderate value of M, (c) high value of M.
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
By varying Ar from 0 to Ac , the pulse width can be varied
from 0 to 180°. Thus, the voltage and hence, the
amount of power sent to the load is controlled. The
modulation index is defined as,
There are many types of PWM, however, the commonly
used techniques for controlling output voltage of a
single-phase inverter are
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
1- Single-pulse width modulation
2- Multiple-pulse-width modulation
3- Sinusoidal pulse-width modulation
4- Modified sinusoidal pulse-width modulation
5- Phase displacement control
Sinusoidal pulse-width modulation (SPWM) is the most
commonly used among all these techniques
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
Single Pulse Width Modulation
This type of modulation gives quasi – square wave
output as shown, according to this figure one can
observe that, there is a single pulse of output voltage
during each half-cycle and the width of the pulse is
varied to control the output voltage
A carrier signal of frequency fc with amplitude Ac is
modulated by another signal or reference signal of
amplitude Ar as shown
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Single
: Pulse Width Modulation
(a) Reference signal,
(b) Gate signals
(c) Output voltage waveform.
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Single
: Pulse Width Modulation
The main objective of using modulation process in power
electronics engineering is to generate the gate signal to
the power switches and thereby determine the output
frequency of the inverter. As mentioned before, the output
voltage can be varied by varying the pulse width δ by
varying the amplitude Ar from 0 to Ac. i.e by varying the
modulation index M from 0 to 1, The rms of the output
voltage is given by
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Single
: Pulse Width Modulation
The output voltage waveform has the Fourier series
The peak value of the fundamental component is
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Single
: Pulse Width Modulation
Pulse width δ has a maximum value of π radians at which
the fundamental term in is a maximum. The nth order
harmonic is seen to have peak value,
The distortion factor of the single-pulse waveform is
therefore
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Single
: Pulse Width Modulation
A single-phase full-bridge voltage source inverter, fed
from 200 V d.c. if single-pulse width modulation
technique with δ = 120 ˚ is used to control the output
voltage Assuming the load is purely resistive, find the rms
value of the output voltage.
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical
and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
Multiple-Pulse Width Modulation
An alternative waveform consisting m symmetrical spaced
pulses per half-cycle can be obtained by control the
output voltage of the inverter such that it can be switched
on and off rapidly several times during each half-cycle to
produce a train of constant magnitude pulses shows the
idea of multiple pulse-width modulation
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
The output voltage waveform consists of p pulses for each
half-cycle of the required output voltage
Minimum pulse width is zero and maximum pulse width
will be π/p Let fo be the output frequency of the inverter,
and T = 1/fo =2π
In this period there are 2p pulses of equal width. The first
pulse is located at π/p, then its width
is to
as depicted in Fig. In this case the rms value of the output
voltage will be
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
The frequency of the pulses is fp = 2pfo which must be the same
frequency of the carrier signal fc that is always greater than the
output frequency fo
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
Thus, the number of equal symmetrical pulses p per
half-cycle can be calculated as
where mf = fc / fo is a factor defined as the frequency
modulation ratio
The Fourier series of the output voltage is found to be
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
The normalized amplitude of harmonics and the
percentage distortion factor variation with the modulation
index M are shown in Fig. for p = 5 of the multiple pulse
modulation.
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control
Multiple-Pulse
:
Width Modulation
A single-phase full-bridge voltage source inverter, fed from
200 V d.c. the strategy of output voltage control is changed
such that the technique used is multiple pulse width
modulation. The width of each pulse is 20˚ and each half
cycle has 6 pulses,
(a) Determine the rms value of the output voltage, (b) Find
the pulse width to maintain the output rms value in (a)
constant if the input voltage increases by 20%, (c) What is
the maximum input voltage if the maximum possible pulse
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical
and
Electronics Engineering
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
Sinusoidal Pulse-Width Modulation (SPWM)
Using sinusoidal reference signal will produce varied width
pulses that proportional to the amplitude of the sine wave
as shown in Fig. In this technique, the lower order
harmonics of the modulated voltage wave are greatly
reduce. The rms value of the output voltage of the inverter
depends on the widths of the pulses (δm).
These widths depend on the modulation index M which
controls the output voltage of the inverter
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
Sinusoidal Pulse-Width Modulation (SPWM)
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
Sinusoidal Pulse-Width Modulation (SPWM)
The magnitude of the fundamental component of the
output
voltage
is
clearly
proportional
to
the
modulation index Ar /Ac But the highest practical value
of M is unity
If Ar ˃ Ac the output voltage waveform vo(ωt) approaches
a rectangular form and undesirable low frequency
harmonics such as the third , fifth and seventh
harmonics are introduced and intensified.
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
Sinusoidal Pulse-Width Modulation (SPWM)
The rms output voltage is
POWER ELECTRONICS
Pulse-width-modulated inverters
Inverter output voltage control :
Sinusoidal Pulse-Width Modulation (SPWM)
Another type of sinusoidal modulation can obtained by
using two anti-phase sinusoidal reference (modulating)
signal as shown in Fig(a). This technique is called
double-sided triangular carrier wave modulation. The
reference signal vra produces the resultant modulated
wave va , Fig.(b), whereas the reference signal vrb
produces the resultant modulated wave vb , Fig. (c). The
corresponding line voltage vab = va -vb has a fundamental
component as shown in Fig.(d)
POWER ELECTRONICS
Pulse-width-modulated inverters
Sinusoidal Pulse-Width Modulation (SPWM)
POWER ELECTRONICS
Pulse-width-modulated inverters
Modified Sinusoidal Pulse Width Modulation
The carrier wave is generated so the widths of the
pulses that are near to the peak of the sine wave not
change much when modulation index changed. Such
scheme is shown in Fig. and known as MSPWM. Note
that the triangular wave is present for the period of
first 60˚ of the half cycle of sine wave. The MSPWM
increase the fundamental component and improve the
harmonic characteristic. This technique reduces the
number of switching of power devices and also
POWER ELECTRONICS
Pulse-width-modulated inverters
Modified Sinusoidal Pulse Width Modulation
POWER ELECTRONICS
Pulse-width-modulated inverters
Modified Sinusoidal Pulse Width Modulation
A single-phase full-bridge voltage source inverter, fed
from 200 V d.c. source. The output voltage is controlled
by sinusoidal pulse width modulation technique. The
carrier and modulating signals are so adjusted that the
modulation index produces three pulses per half a cycle
of widths, 20˚, 60˚, and 20˚. Assuming the load is
purely resistive, find the rms value of the output voltage
POWER ELECTRONICS
Pulse-width-modulated inverters
Phase-displacement control
POWER ELECTRONICS
Pulse-width-modulated inverters
Phase-displacement control
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
Controlled rectifiers are line commutated ac to dc power
converters which are used to convert a fixed voltage, fixed
frequency ac power supply into variable dc output voltage
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
The input supply fed to a controlled rectifier is ac supply at a fixed
rms voltage and at a fixed frequency to obtain variable dc output
voltage by using controlled rectifiers. By employing phase
controlled thyristors in the controlled rectifier circuits for obtain
variable dc output voltage and variable dc (average) output current
by varying the trigger angle (phase angle) at which the thyristors
are triggered, obtain a uni-directional and pulsating load current
waveform, which has a specific average value
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
The load current flows when the thyristors conduct from wt=α to β
The output voltage across the load follows the input supply voltage
through the conducting thyristor
At wt=β , when the load current falls to zero, the thyristors turn off
due to AC line (natural) commutation, When the input ac supply
voltage reverses and becomes negative during the negative half
cycle, the thyristor becomes reverse biased and hence turns off
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
Applications of phase controlled rectifiers
• DC motor control in steel mills, paper and textile mills employing dc
motor drives.
• AC fed traction system using dc traction motor.
• Electro-chemical and electro-metallurgical processes.
• Magnet power supplies.
• Reactor controls.
• Portable hand tool drives.
• Variable speed industrial drives.
• Battery charges.
• High voltage DC transmission.
• Uninterruptible power supply systems (UPS).
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
Half wave controlled rectifier, which uses a single thyristor
device (which provides output control only in one half cycle of
input ac supply, and it provides low dc output).
The basic principle of operation of a phase controlled rectifier
circuit is explained with reference to a single phase half wave
phase controlled rectifier circuit with a resistive load
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
During the positive half cycle of input supply when the upper end of
the transformer secondary is at a positive potential with respect to
the lower end, the thyristor anode is positive with respect to its
cathode and the thyristor is in a forward biased state
The thyristor is triggered at a delay angle of wt=α , by applying a
suitable gate trigger pulse to the gate lead of thyristor. When the
thyristor is triggered at a delay angle of α , the thyristor conducts
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
To derive an expression for the average (dc) output voltage across
the load
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
The average dc output voltage is given by the expression
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
To derive an expression for the rms value of output voltage of a single
phase half wave controlled rectifier with resistive load
POWER ELECTRONICS
Controlled rectifiers
Principle of phase-controlled converter operation:
POWER ELECTRONICS
Controlled rectifiers
What will be the average power in the load for the circuit
shown, when α=(π/4) Assume SCR to be ideal. Supply voltage
is Vs=330 sin314t. Also calculate the RMS power and the
rectification efficiency
POWER ELECTRONICS
Controlled rectifiers
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
Form Factor (FF) which is a measure of the shape of the
output voltage is given by
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
The Ripple Factor (RF) which is a measure of the ac ripple
content in the output voltage waveform. The output voltage
ripple factor defined for the output voltage waveform is given
by
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
Transformer Utilization Factor (TUF)
Vs = RMS value of transformer secondary output voltage (RMS
supply voltage at the secondary)
Is = RMS value of transformer secondary current (RMS line or
supply current).
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
Displacement Factor (DF) or Fundamental Power Factor
DF=Cosφ
Harmonic Factor (HF) or Total Harmonic Distortion Factor (THD)
The harmonic factor is a measure of the distortion in the output
waveform and is also referred to as the total harmonic distortion
(THD)
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
Disadvantages of single phase half wave controlled rectifiers:
Low dc: output voltage, output power and lower efficiency. Higher
ripple voltage, ripple current and ripple factor. Low transformer
utilization factor.
The input supply current waveform has a dc
component which can result in dc saturation of the transformer core
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
The single-phase half-wave controlled rectifier (a) supplies a
resistive load draws an average current of 1.62 A. If the converter
is operated from a 240 V, 50 Hz supply and if the average value of
the output voltage is 81V, calculate the following:
(a) The firing angle α.
(b) Load resistance .
(c)The
(d) The rms load current.
rms load voltage.
(e) DC power.
(f) The ripple factor
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
The circuit is used as a half-wave controlled rectifier supplying
resistive load with RL = 1k and Vs=240V. For the firing angles
obtained in the load current waveforms for both angles and determine
the corresponding power dissipation in the load resistor.
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
A single-phase half-wave controlled rectifier supplied from 230V
a.c. supply is operating at α = 60° If the load resistor is 10Ω ,
determine:
(a) The power absorbed by the load (Pdc).
(b) The power (Pac).
(c) The power factor at the a.c. source
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
2127.9W
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
An SCR is used to control the power of 1kW, 230V, 50Hz heater
Determine heater power for firing angles of 45° and 90°
From the given data R=52.9Ω, hence at 45°, power ( rms voltage)
is 454.15W and at 90° it is 250W
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
1 phase half-wave controlled converter is operated from a 120V, 50Hz
supply, R=10Ω. If the average output voltage is 25% of the max. possible
avg. out put voltage Determine: a)firing angle b)rms and avg output
current
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
An SCR is used to control the power of 1kW, 230V, 50Hz heater
Determine heater power for firing angles of 45° and 90°
From the given data R=52.9Ω, hence at 45°, power ( rms voltage)
is 454.15W and at 90° it is 250W
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
1 phase half-wave controlled converter is operated from a 120V, 50Hz
supply, R=10Ω. If the average output voltage is 25% of the max. possible
avg. out put voltage Determine: a)firing angle b)rms and avg output
current
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
POWER ELECTRONICS
Controlled rectifiers
Performance parameters of phase controlled rectifiers
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
The two thyristors are controlled power switches which are turned
on one after the other by applying suitable gating signals
The two diodes are uncontrolled power switches which turn-on
and conduct one after the other as and when they are forward
biased. The circuit diagram is shown in the above figure with highly
inductive load and a dc source in the load circuit. When the load
inductance is large the load current flows continuously
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
Waveforms of single phase semi-converter for
RLE load and constant load current for α > 90°
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
To derive an expression for the average or dc output voltage of a
single phase semi-converter
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
1 phase semi-converter is operated from 120V, 50Hz AC supply.
The load resistance is 10Ω, If the average output voltage is 25%
of max. possible average output voltage, determine
a)Firing angle b) rms and avg. output current
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
POWER ELECTRONICS
Controlled rectifiers
Single-phase semi converters:
A single phase semi-converter is operated from 120V, 50Hz AC supply
The load current with an avg. value Idc is continuous and ripple free
𝜋
firing angle α= determine a) Displacement factor
6
b) Harmonic factor of input current c) input PF
Ans: a) DF=0.9659 b) HF=30.8% c)0.922(lag)
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
A single-phase full-wave fully-controlled bridge rectifier is feeding an R-L
load with R = 15Ω and L = 20 mH. The rms value of the a.c. input voltage
is 230 V. The firing angle α is maintained constant at 45⁰ , (a) Determine
the average load voltage Vdc and current Idc. (b) Assume that load
resistance remains the same; find the voltage Vdc and current Idc . if a
freewheeling diode DFW is used across the load. (c) If T3 is open
circuited, find the load voltage and d.c. power while freewheeling diode
DFW is still connected and α is the same.
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
When the freewheeling diode DFW is used across
the load, and the load resistance remains the
same
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
1 phase fully controlled converter with inductive load. Assuming that
the output current is virtually constant, voltage 230V and firing angle
is 30° Determine: i) Avg. output voltage ii) supply rms current iii)
supply fundamental rms current iv)Fundamental PF v) Supply PF
vi)Supply HF vii)Voltage RF
Ans: 179.33V, ii) Id iii)
2√2
Id
𝜋
iv) 0.86 v) 0.78 vi) 0.483 vii) 0.803
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
In the circuit shown find out the average voltage across the load
assuming that the conduction drop across the SCR is 1 volt.
Take α = 45°.
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
In the figure find out the battery charging current when, Assume
ideal SCR α=45°
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
It is obvious that the SCR cannot conduct when the instantaneous
value of the supply voltage is less than 24 V, the battery voltage.
The load voltage waveform is as shown .
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
A single phase full wave controlled rectifier is used to supply a
resistive load of 10 Ω from a 230 V, 50 Hz, supply and firing angle
of 90°. What is its mean load voltage? If a large inductance is
added in series with the load resistance, what will be the new
output load voltage?
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
When a large inductance is added in series with the load, the
output voltage wave form will be as shown below, for trigger angle
α=90°
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
The figure shows a battery charging circuit using SCRs. The input
voltage to the circuit is 230 V RMS. Find the charging current for a
firing angle of 45°. If any one of the SCR is open circuited, what is
the charging current?
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
POWER ELECTRONICS
Controlled rectifiers
Single phase full converter (fully controlled bridge converter)
If one of the SCRs is open circuited, the circuit behaves like a
half wave rectifier. The average voltage across the resistance
and the charging current will be half of that of a full wave
rectifier.
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
The dual converter system will provide four quadrant operation. The
converter number 1 provides a positive dc output voltage and a
positive dc load current, when operated in the rectification mode.
The converter number 2 provides a negative dc output voltage and a
negative dc load current when operated in the rectification mode.
The magnitude of output dc load voltage and the dc load current can
be controlled by varying the trigger angles of the converters 1 and 2
respectively α1 and α2
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
There are two modes of operations possible for a dual converter
system.
• Non circulating current mode of operation (circulating current
free mode of operation).
• Circulating current mode of operation
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
Non circulating current mode of operation (circulating current
free mode of operation)
In this mode of operation only one converter is switched on at a time
while the second converter is switched off. When the converter 1 is
switched on and the gate trigger signals are released to the gates of
thyristors in converter 1, get an average output voltage across the
load, which can be varied by adjusting the trigger angle α1 of the
converter 1.
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
If α1 is less than 90°, the converter 1 operates as a controlled rectifier
and converts the input ac power into dc output power to feed the
load and are both Vdc and Idc positive and the operation occurs in the
first quadrant. The average output power is positive. The power
flows from the input ac supply to the load. When α1 is increased
above 90° converter 1 operates as a line commutated inverter and
Vdc becomes negative while Idc is positive and the output power
becomes negative
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
The power is fed back from the load circuit to the input ac source
through the converter 1. The load current falls to zero when the
load energy is utilized completely.
The second converter 2 is switched on after a small delay of about
10 to 20 mill seconds to allow all the thyristors of converter 1 to
turn off completely. The gate signals are released to the thyristor
gates of converter 2 and the trigger angle α2 is adjusted such that
0 ≤ α2 ≤90° so that converter 2 operates as a controlled rectifier
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
The advantage of non circulating current mode of operation is that
there is no circulating current flowing between the two converters
as only one converter operates and conducts at a time while the
other converter is switched off. Hence there is no need of the
series current limiting inductors between the outputs of the two
converters. The current rating of thyristors is low in this mode. But
the disadvantage is that the load current tends to become
discontinuous and the transfer characteristic becomes non linear
POWER ELECTRONICS
Controlled rectifiers
Single – phase dual converters:
The control circuit becomes complex and the output response is
sluggish as the load current reversal takes some time due to the
time delay between the switching off of one converter and the
switching on of the other converter. Hence the output dynamic
response is poor. Whenever a fast and frequent reversal of the
load current is required, the dual converter is operated in the
circulating current mode
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
In this mode of operation both the converters 1 and 2 are switched
on and operated simultaneously and both the converters are in a
state of conduction. If converter 1 is operated as a controlled
rectifier by adjusting the trigger angle α1 between 0 to 90° the
second converter 2 is operated as a line commutated inverter by
increasing its trigger angle α2 above 90°. The trigger angles α1 and α2
are adjusted such that they produce the same average dc output
voltage across the load terminals
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
The average dc output voltage of converter 1 and 2
In the dual converter operation one converter is operated as a
controlled rectifier with α1 < 90° and the second converter is
operated as a line commutated inverter in the inversion mode
with α2 > 90°
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
When the trigger angle α1 of converter 1 is set to some value the
trigger angle α2 of the second converter is adjusted such that
α2=(180°- α1). Hence for circulating current mode of operation where
both converters are conducting at the same time (α1+ α2=180°) so
that they produce the same dc output voltage across the load
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
In the circulating current mode a current builds up between the
two converters even when the load current falls to zero. In order to
limit the circulating current flowing between the two converters,
we have to include current limiting reactors in series between the
output terminals of the two converters. The advantage of the
circulating current mode of operation is that we can have faster
reversal of load current as the two converters are in a state of
conduction simultaneously.
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
This greatly improves the dynamic response of the output giving a
faster dynamic response. The output voltage and the load current
can be linearly varied by adjusting the trigger angles α1 and α2 to
obtain a smooth and linear output control. The control circuit
becomes relatively simple. The transfer characteristic between the
output voltage and the trigger angle is linear and hence the output
response is very fast. The reversal of the load current can be done in
a faster and smoother way
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
The disadvantage of the circulating current mode of operation is
that a current flows continuously in the dual converter circuit even
at times when the load current is zero. Hence we should connect
current limiting inductors (reactors) in order to limit the peak
circulating current within specified value. The circulating current
flowing through the series inductors gives rise to increased power
losses, due to dc voltage drop across the series inductors which
decreases the efficiency.
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
Also the power factor of operation is low. The current limiting
series inductors are heavier and bulkier which increases the cost
and weight of the dual converter system. The current flowing
through the converter thyristors is much greater than the dc load
current, If VO1 and VO2 are the instantaneous output voltages of the
converters 1 and 2, respectively the circulating current can be
determined by integrating the instantaneous voltage difference
(which is the voltage drop across the circulating current reactor Lr),
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
starting from ωt = (2π- α1). As the two average output voltages
during the interval ωt = (π+ α1) to (2π- α1) are equal and opposite
their contribution to the instantaneous circulating current ir is zero
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
To calculate the circulating current
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
POWER ELECTRONICS
Controlled rectifiers
Circulating current mode of operation :
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
Features of 3-phase controlled rectifiers are:
• Operate from 3 phase ac supply voltage
• They provide higher dc output voltage and higher dc
output power.
• Higher output voltage ripple frequency.
• Filtering requirements are simplified for smoothing out
load voltage and load current
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
Three phase full converter is a fully controlled bridge controlled
rectifier using six thyristors connected in the form of a full wave
bridge configuration. All the six thyristors are controlled switches
which are turned on at a appropriate times by applying suitable
gate trigger signals. The three phase full converter is extensively
used in industrial power applications upto about 120kW output
power level, where two quadrant operation is required.
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
The thyristors are triggered at an interval of π/3 radians
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
The thyristors are numbered in the circuit diagram corresponding
to the order in which they are triggered. The trigger sequence
(firing sequence) of the thyristors is 12, 23, 34, 45, 56, 61, 12, 23,
and so on.
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
The maximum average dc output voltage is obtained for a
delay angle α = 0,
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
𝑉𝑜(𝑟𝑚𝑠) = 𝑉𝑚𝑙
3 𝜋
3
+
𝑐𝑜𝑠2𝛼
2𝜋 3
2
1ൗ
2
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
A 3-phase fully-controlled controlled converter charges a
battery from a 3-phase supply of 230V, 50Hz. The battery emf
is 200V and its internal resistance is 0.5Ω , on inductance is
connected in series with battery, charging current is at 20A.
Calculate i) firing angle ii) supply PF b) In case it is desired that
power flows from dc source to ac load in above , find the firing
angle for the same current
Vo=210V, α=47.46° second case Vo=-190V, α=127.71°
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
A 3Ø fully controlled rectifier feeds a power to resistive load of 10Ω
for firing angle delay 30°. The load take 5kW, find i) magnitude of
supply voltage ii) Voltage per phase
Repeat above part, in case a large reactor is in series with load,
which makes the load current ripple free.
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
Vm is obtained from Vo(rms) is 265.98127V, hence Vs=188.077V
and Vph=108.58V
Case 2, Vo(rms)=Vo(avg)=223.606V, Vm=270.384V, Vs=191.19V
Vs(ph)=110.38V
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
3Ø, fully controlled rectifier, operated from 3Ø, star connected
supply with 208V, 60Hz, load R=10Ω, if it is required to obtained
max. of 50% of possible output voltage, calculate
i) Delay angle ii) rms and avg. current iii) efficiency of rectifier
Ans: i) 60°, ii)15.929A & 14.0449A iii) 77.71%
POWER ELECTRONICS
Controlled rectifiers
Three-phase full converters with RL load:
A three-phase controlled rectifier has an input voltage which is
480Vrms at 60 Hz. The load is modeled as a series resistance and
inductance with R=10 Ω and L=50mH. Determine the delay angle
required to produce an average current of 50 A in the load
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Phase-controlled operation in both single phase full wave half and full
controlled bridge converters, the displacement factor (or power
factor, which is lagging) decreases, as the average value of output
voltage (Vdc) decreases, with the increase in firing angle delay, α. The
three schemes used for power factor (PF) improvement are:
• Extinction angle control
• Symmetrical angle control
• Pulse width modulation (PWM) control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Power factor (PF) in controlled rectifier is depends on delay angle α
and it is low at low output voltage range, these converters
generates harmonics in to the supply. Forced commutation can
improve the input PF and reduce the harmonics level. Single phase
semi-converter with S1 and S2 , GTOs are the preferable choice, since
GTOs can be turned on with +ve pulse to its gate and they can be
turned off with –ve gate pulse
In extinction angle control, switch, S1 is turned on at ωt=0, and then
turned off by forced commutation at ωt=(π−β)
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
extinction angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
extinction angle control
The switch, S2 is turned on at ωt=π, and then turned off at ωt=(2π−β)
The output voltage is controlled by varying the extinction angle, β. Fig.
shows the waveforms for input voltage, output voltage, input current,
and the current through thyristor switches. The fundamental
component of input current leads the input voltage, and the
displacement factor (and power factor) is leading. This feature may be
desirable to simulate a capacitive load, thus compensating the line
voltage drops
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
extinction angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
extinction angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
This control can be applied for the same half-controlled force
commutated bridge converter with two switches, S1 and S2 as shown in
Fig. The switch, S1 is turned on at ωt=(π−β)/2 and then turned off at
ωt=(π+β)/2 . The other switch, S2 is turned on at ωt=(3π−β)/2 and
then turned off at ωt=(3π+β)/2. The output voltage is varied by
varying conduction angle, β. The gate signals are generated by
comparing half-sine waves with a dc signal as shown in Fig.
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
The half-sine waves can be obtained using a full wave diode
(uncontrolled) bridge converter. In the second case, the conduction
angle varies linearly with the dc signals, but in inverse ratio, i.e.,
when the dc signal is zero, full conduction (β=π) takes place, and
the dc signal being same as the peak of the triangular reference
signal, no conduction (β=0) takes place. Fig. shows the waveforms
for input voltage, output voltage, input current and the current
through the switches.
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
The fundamental component of input current is in phase with
input voltage, and the displacement factor is unity (1.0).
Therefore, the power factor is improved.
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
1-phase full converter with symmetrical angle control, load current Ia
is continuous and ripple free, a) express input current in Fourier
series and Find HF, DF and input PF
b) Take conduction angle β=60° and peak input voltage is 169.83V,
calculate Vdc, Vrms, HF, DF and PF
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
POWER ELECTRONICS
Controlled rectifiers
Power factor improvement :
Symmetrical angle control
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
The basic principle of ON-OFF control technique is explained with
reference to a single phase full wave ac voltage controller circuit. The
switches T1 and T2 are turned ON by applying appropriate gate trigger
pulses to connect the input ac supply to the load for ‘n’ number of
input cycles during the time interval TON. Turned OFF by blocking the
gate trigger pulses for ‘m’ number of input cycles during the time
interval TOFF. The AC controller ON time TON usually consists of an
integral number of input cycles
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
POWER ELECTRONICS
AC voltage controllers, current control and applications
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
Thyristors are turned ON during on t for two input cycles. m = One
input cycle. Thyristors are turned OFF during off t for one input cycle.
The load current flows in the positive direction, when T1 conducts.
The thyristor T2 is turned on at the beginning of each negative half
cycle, by applying gating signal to the gate of T2 , during TON . The load
current flows in the reverse direction, whenT2 conducts. Thus obtain
a bi-directional load current flow (alternating load current flow) in a
ac voltage controller circuit, by triggering the thyristors alternately
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
Due to zero voltage and zero current switching of Thyristors, the
harmonics generated by switching actions are reduced
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
To derive an expression for the rms value of output voltage, for on-off
control method
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
Performance parameters of ac voltage controllers
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control:
Performance parameters of ac voltage controllers
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of On-OFF control:
Performance parameters of ac voltage controllers
Duty Cycle
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control: Input Power Factor
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of On-OFF control: The average current of thyristor
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON-OFF control: The average current of Thyristor
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON- OFF control:The RMS current of Thyristor
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of ON- OFF control:Applications of AC voltage controller
• Speed control of induction motor (polyphase ac induction
motor).
• Heater control circuits (industrial heating).
• Welding power control.
• Induction heating.
• On load transformer tap changing.
• Lighting control in ac circuits.
• AC magnet controls
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of on-off control:
A single phase full wave ac voltage controller working on ON-OFF
control technique has supply voltage of 230V, RMS 50Hz, load = 20Ω
The controller is ON for 10 cycles and off for 4 cycles. Calculate:
• RMS output voltage.
Ans: Vo(rms)=194.385V
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of on-off control:
A single phase full wave ac voltage controller working on ON-OFF
control technique has supply voltage of Vs= 220 sinwt, load = 20Ω, it
is ON for 30% of the maximum, its base period is 20 cycles.
Calculate:
• RMS output voltage and power dissipated at the load
Ans: Vo(rms)=85.2056V and Po=363W
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of on-off control:
A single phase full wave ac voltage controller working on ON-OFF
control technique has supply voltage of 230V, RMS 50Hz, load = 50Ω
The controller is ON for 30 cycles and off for 40 cycles. Calculate:
• ON & OFF time intervals.
• RMS output voltage.
• Input P.F.
• Average and RMS thyristor currents.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of on-off control:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of on-off control:
Average Thyristor Current Rating
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of AC phase control :
The basic principle of AC phase control technique is explained with
reference to a single phase half wave AC voltage controller
(unidirectional controller) circuit
The half wave AC controller uses one thyristor and one diode
connected in parallel across each other in opposite direction that is
anode of thyristor T1 is connected to the cathode of diode D1 and the
cathode of T1 is connected to the anode of D1 (anti-parallel)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of AC phase control :
The output voltage across the load resistor ‘R’ and hence the AC
power flow to the load is controlled by varying the trigger angle ‘α’
The trigger angle or the delay angle ‘α’ refers to the value of ωt or
the instant at which the thyristor T1 is triggered to turn it ON, by
applying a suitable gate trigger pulse between the gate and cathode
lead. The thyristor T1 is forward biased during the positive half cycle
of input AC supply
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of AC phase control :
It can be triggered and made to conduct by applying a suitable gate
trigger pulse only during the positive half cycle of input supply
When T1 is triggered it conducts and the load current flows through
the thyristor T1 , the load and through the transformer secondary
winding. By assuming T1 as an ideal thyristor switch it can be
considered as a closed switch when it is ON during the period
ωt =α to π radians.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Principle of AC phase control :
The output voltage across the load follows the input supply voltage
when the thyristor T1 is turned-on and when it conducts from ωt =α
to π radians. When the input supply voltage decreases to zero at
ωt =π , for a resistive load the load current also falls to zero at ωt =π
and hence the thyristor T1 turns off at ωt =π. Between the time
period ωt = π to 2π, when the supply voltage reverses and becomes
negative the diode D1 becomes forward biased and hence turns ON
and conducts
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller)
The load current flows in the opposite direction during ωt = π to 2π
radians, when D1 is ON and the output voltage follows the negative
half cycle of input supply
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller)
Observe from the control characteristics the given above that the
range of RMS output voltage control is from 100% of Vs to 70.7% of
Vs. Vary the trigger angle α from zero to 180 degrees.
Thus the half wave AC controller has the draw back of limited range
RMS output voltage control
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller):
To calculate the average value (DC value) of output voltage
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller):
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller):
POWER ELECTRONICS
AC voltage controllers, current control and applications
Half wave AC phase controller (unidirectional controller):
RMS thyristor current can be calculated by using the expression Io(rms):
POWER ELECTRONICS
AC voltage controllers, current control and applications
Disadvantages of single phase half wave AC voltage controller
The half wave AC voltage controller using a single thyristor and a
single diode provides control on the thyristor only in one half cycle of
the input supply
Hence AC power flow to the load can be controlled only in one half
cycle, Half wave AC voltage controller gives limited range of RMS
output voltage control
POWER ELECTRONICS
AC voltage controllers, current control and applications
Disadvantages of single phase half wave AC voltage controller
Because the RMS value of AC output voltage can be varied from a
maximum of 100% of Vs at a trigger angle α = 0 to a low of 70.7%
of Vs at α =π radians
These drawbacks of single phase half wave ac voltage controller
can be overcome by using a single phase full wave ac voltage
controller
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase half wave AC voltage controller:
A single phase half wave ac regulator using one SCR in anti-parallel
with a diode feeds 1 kW, 230 V heater. Find load power for a firing
angle of 45°. Find IT(avg),IT(rms)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase half wave AC voltage controller:
Single phase half wave AC voltage controller has R=5Ω, Vs=120V,
𝜋
50Hz, α=
Determine: i) Vo(rms) ii) PF iii) Vo(avg)
3
Ans: 113.98V 0.9 and -13.5V
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
Single phase full wave AC voltage controller (Bi-directional
Controller)using SCRs
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
The thyristor T1 is forward biased during the positive half cycle of
the input supply voltage. The thyristor T1 is triggered at a delay
angle of 'α '(0 ≤α ≤π radians) . Considering the ON thyristor T1 as
an ideal closed switch the input supply voltage appears across the
load resistor RL and the output voltage VO = V during ωt =α to π
radians
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
The load current flows through the ON thyristorT1 and through the
load resistor RL in the downward direction during the conduction
time of T1 from ωt =α to π radians. At ωt =π , when the input
voltage falls to zero the thyristor current (which is flowing through
the load resistor RL ) falls to zero and hence T1 naturally turns off
No current flows in the circuit during ωt =π to (π +α )
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
The thyristor T2 is forward biased during the negative cycle of input
supply and when thyristor T2 is triggered at a delay angle (π +α ),
the output voltage follows the negative half cycle of input from ωt
= (π +α ) to 2π . When T2 is ON, the load current flows in the
reverse direction (upward direction) through T2 during ωt = (π +α )
to 2π radians. The time interval (spacing) between the gate trigger
pulses of T1 and T2 is kept at π radians or 180°
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
At ωt = 2π the input supply voltage falls to zero and hence the
load current also falls to zero and thyristor T2 turn off naturally
Instead of using two SCR’s in parallel, a TRIAC can be used for full
wave AC voltage control
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
Maximum RMS voltage will be applied
to the load when, in that case the full
sine wave appears across the load.
RMS load voltage will be the same as
the RMS supply voltage. When is
increased the RMS load voltage
decreases α=0 then Vo(rms)= Vs
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
Need For Isolation
In the single phase full wave ac voltage
controller circuit using two SCRs or Thyristors
in parallel, the gating circuits (gate trigger
pulse generating circuits) of Thyristors must
be isolated. Figure shows a pulse transformer
with two separate windings to provide
isolation between the gating signals
Pulse Transformer
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
A single phase full wave controller has an input voltage of 120 V
(RMS) and a load resistance of 6 ohm. The firing angle of thyristor
is π/2. Find
a. RMS output voltage
b. Power output
c. Input power factor
d. Average and RMS thyristor current
Vo(rms)=84.85V, Po=1.2kW PF=0.707 IT(avg)=4.5A IT(rms)=10A
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with resistive load
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator)
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator)
A single phase half-wave ac voltage controller has a load resistance
R=50Ω, input ac supply voltage is 230V RMS at 50Hz. The input
supply transformer has a turns ratio of 1:1. If the thyristor is
triggered at α=60°. Calculate:
• RMS output voltage.
• Output power.
• RMS load current and average load current.
• Input power factor.
• Average and RMS thyristor current
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator)
Vo(rms)=218.47V Io(rms)=4.36939A Po=954.6W PF=0.9498
Vo(avg)=-25.8844V,Io(avg)=-0.517A, IT(avg)=1.55A and IT(rms)=2.917A
1-phase full-wave AC voltage controller with R=10Ω and
Vs=120V,60Hz. The delay angles for T1 &T2 is 90°, Determine
i) Vo(rms) ii)PF iii)IT(avg)iv) IT(rms)
Ans: 84.85V 0.707
2.7A
6A
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller (AC regulator) or
rms voltage controller with R-L load
Single phase full wave ac voltage controller with RL load
Input supply voltage & Thyristor current waveforms
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller controller with R-L load
Gating Signals
Waveforms of Input supply voltage, Load Current, Load Voltage
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller controller with R-L load
Thyristor voltage across T1
POWER ELECTRONICS
AC voltage controllers, current control and applications
Single phase full wave AC voltage controller controller with R-L load
The RMS value of the output voltage and the load current may be
varied by varying the trigger angle α . For very large load inductance ‘L’
the SCR may fail to commutate, after it is triggered and the load
voltage will be a full sine wave (similar to the applied input supply
voltage and the output control will be lost) as long as the gating signals
are applied to the thyristors T1 and T2 . The load current waveform will
appear as a full continuous sine wave and the load current waveform
lags behind the output sine wave by the load power factor angle φ
POWER ELECTRONICS
AC voltage controllers, current control and applications
To derive an expression for rms output voltage Vo(rms ) of a
single phase full-wave ac voltage controller with R-L load
POWER ELECTRONICS
AC voltage controllers, current control and applications
To derive an expression for rms output voltage Vo(rms ) of a
single phase full-wave ac voltage controller with R-L load
POWER ELECTRONICS
AC voltage controllers, current control and applications
To derive an expression for rms output voltage Vo(rms ) of a
single phase full-wave ac voltage controller with R-L load
The RMS output voltage across the load can be varied by changing
the trigger angle α
POWER ELECTRONICS
AC voltage controllers, current control and applications
To derive an expression for rms output voltage Vo(rms ) of a
single phase full-wave ac voltage controller with R-L load
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
A single phase voltage controller is employed for controlling the
power flow from 220 V, 50 Hz source into a load circuit consisting
of R = 4Ω and ωL = 6Ω. Calculate the following:
a. Control range of firing angle
b. Maximum value of RMS load current
c. Maximum power and power factor
d. Maximum value of average and RMS thyristor current
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Performance parameters of a single phase full wave AC voltage
controller with R-L load:
Single phase , bidirectional AC regulator, Vs=230V, R=2Ω, XL=2Ω and
α1= α2=π/2, Find the rms output voltage and extinction angle β
Ans: β=220.86°
Single phase , bidirectional AC regulator, Vs=120V,60Hz, R=2.5Ω,
L=6.5mH and α1= α2=π/2, Find:
i) rms output voltage and extinction angle β ii)Vo(rms) iii)Io(rms) iv) PF
Ans: 220.35°
68.09V
15.07A 0.444
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Initially V2 is impressed across the load, via T3 (T4). Turning on T1 (T2)
reverse-biases T3 (T4), hence T3 (T4) turns off and the load voltage
jumps to V1. It is possible to vary the rms load voltage between V2 and
V1. It is important that T1 (T2) and T4 (T3) do not conduct
simultaneously, since such conduction short circuits the transformer
secondary.
Both load current and voltage information (specifically zero crossing)
is necessary with inductive and capacitive loads, if winding short
circuiting is to be avoided
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
In this use set of thyristor connected antiparallel means four
thyristor in this circuit. The source voltage will provide the ac
voltage which will consist of primary winding and secondary
winding. The secondary winding will be center tapped the two
winding will be mutual connected. The voltage from the one
winding will be V1= Vm sinωt and voltage across second winding will
V2= Vm sinωt
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
The thyristor T3 and T4 will only work when the ωt=0 means when the
firing angle ⍺ will be equal to zero. The thyristor T1 and T2 will work
when at particular angle the pulse is provide means there firing angle
will be at certain phase. When start the supply from the source voltage
when positive cycle will occur and ωt=0 then thyristor3 will conduct and
the current will pass from thyristor3.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
The voltage will be from the secondary winding V2 and the source
current will flow from thyristor T3 when ⍺ will be equal to zero when
the ωt will be equal to ⍺ then provide trigger pulse at the gate of T1
then thyristor3 will off and thyristor1 will conduct at this time then
the voltage will be from V1+V2 and the source current will flow in T1
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
The wave will go in upward direction after trigger pulse. This is because
first there is only one voltage which was V1 and now there two voltages
which are V1+V2 the complete secondary winding will work
When a negative cycle will come from the source the primary and lower
secondary will start working the voltage will be V2 when provide trigger
pulse at T4 it will start conducting
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
The output voltage will be in reverse direction and the ωt=π. The output
current will be also in reverse direction. When a trigger pulse will be
given at the gate of the T2 then the output voltage will be equal to V1+V2.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
A two stage sequence control of ac voltage controller employs two
stages in parallel as shown above
The turns ratio from primary to secondary is taken as unity for
convenience
The main advantage of two-stage sequence control of ac voltage
controller over single phase full-wave ac voltage controller is the
reduction of harmonics in the load and supply currents
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
For resistive load current waveform is identical with the output
voltage waveform when thyristor pairT3,T4 is in operation T1,T2 off rms
value of output voltage
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
A connector changer with this type of control is known as a
synchronous connection changer. It uses two-step control, a part of
secondary voltage V2 is super imposed on a sinusoidal voltage V1, as a
result, the harmonic contents are less than those that would be
obtained by a normal phase delay
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
Two stage sequence control AC voltage controller with R load:
1 2𝜋 2
𝑉0 =
න 𝑉 𝑑(𝑤𝑡)
2𝜋 0
𝑉𝑜 =
1
2
𝜋
2 𝛼
න 2 𝑉1 2 𝑠𝑖𝑛2 𝑤𝑡𝑑 𝑤𝑡 + න 2(𝑉1 + 𝑉2 )2 𝑠𝑖𝑛2 𝑤𝑡 𝑑(𝑤𝑡)
2𝜋 0
𝛼
𝑉𝑜𝑟𝑚𝑠 =
𝑉1 2
𝑠𝑖𝑛2𝛼
𝑉1 + 𝑉2
𝛼−
+
𝜋
2
𝜋
2
𝑠𝑖𝑛2𝛼
𝜋−𝛼+
2
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
The single phase transformer tap changer has the primary voltage
of 260V(rms) 50Hz, The secondary voltages are e1=130V and
e2=130V, if the load resistance R=6Ω, the rms load voltage is 195V
and the firing angle of thyristors T1 and T2 is 90°, determine
a) rms current of T1 & T2
b) rms current of T3 & T4
c) Output power
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
𝜋
1
2 𝑠𝑖𝑛2 𝑤𝑡 𝑑(𝑤𝑡)
න
2(𝑒
+
𝑒
)
1
2
2𝜋𝑅2 𝛼
𝐼1 =
𝐼1 = 21.67𝐴 = 𝑇ℎ𝑦. 𝑟𝑚𝑠 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑜𝑓 𝑇1&𝑇2
𝐼2 =
𝜋/2
1
2 𝑠𝑖𝑛2 𝑤𝑡 𝑑(𝑤𝑡)
න
2(𝑒
)
1
2𝜋𝑅2 0
𝐼2 = 10.83𝐴 = 𝑇ℎ𝑦. 𝑟𝑚𝑠 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑜𝑓 𝑇3&𝑇4
𝐸𝑜 2
𝑃𝑜 =
= 6337.5𝑊
𝑅
POWER ELECTRONICS
AC voltage controllers, current control and applications
Transformer tap changing:
If the primary voltage is 240V , V1=120V and V2=120V, R=10 and the
rms load voltage 180V. calculate delay angle of T1 & T2
of T1 and T2 and rms currents of T3 and T4
α=98° from iterative method or from graph, 10.9A and 6.5A
rms currents
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
The general implementation of hysteretic current-mode control is
shown in Fig.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
The inductor current waveforms are used to control both the turn-on
and the turn-off of the power switch of the PWM converter
The advantages of this kind of circuit, no clock or timing function is
needed, and the current level is controlled between two limits,
Although this implementation was popular before control circuits
became available, its variable switching frequency, and the need to
sense the inductor current during both the on- and off-times of the
power switch
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
A hysteretic switching regulator also called a ripple regulator the
simplest switching structure. In essence, this is an unstable system
whose toggling period depends on the various time constants
involved in the circuit. There is no internal clock and the system is
self-relaxing.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
hysteretic switching buck regulator
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
As in most comparator-based circuits, hysteresis is used to maintain
predictable operation
This architecture continuously shuttles the output voltage back and
forth to just above or below the ideal set point.
Because the
hysteretic architecture varies, the drive signal to the power MOSFET is
based on the operating conditions of the circuit
The switching frequency is not constant
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
Hysteretic control converter turns the power MOSFET on or off
based on the output voltage changes sensed by the converter
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
The advantages of hysteretic control:
• No loop compensation required. The loop bandwidth is close to
the switching frequency itself
• No clock or error amplifier is needed, so operating current is very
low, this type of regulator is suitable for battery-powered applications
• Hysteretic converters are low cost
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
The hysteretic control disadvantages:
• With no fixed clock, it is difficult to predict switching frequency
compared to PWM control
• This type of regulator is not suitable for applications with
sensitive analog circuitry
• May require a feed-forward capacitor across R1 to increase
voltage ripple on the feedback pin when using lower-ESR output
capacitors
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
Hysteretic constant on-time (COT) control keeps frequencies
constant:
The main disadvantage of the hysteretic converter is the variable
frequency. Because it uses a comparator with hysteresis, there must
be sufficient voltage ripple at the feedback node to ensure stable
switching. Basically, the ripple voltage at the comparator’s feedback
node must be greater than the comparator’s hysteresis band
Moreover, a higher ESR capacitor may be needed to increase output
ripple voltage or a feed-forward capacitor must be added
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
Hysteretic constant on-time (COT) control keeps frequencies
constant(cont.):
To keep the frequency as constant as possible, a constant on-time (COT)
generator has been added. In this COT control mode, the TON time will
be inversely proportional to the input voltage
The COT generator greatly enhances this type of converter, allowing it to
maintain a constant frequency over a wider range of input voltages
The generator, however, does not solve the need to add ripple at the
feedback node to help the comparator switch
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
The addition of COT to hysteretic control lets the design engineer
better predict the switching frequency. COT control also lets a better
optimize filtering for EMI and offers the advantage of low cost and
good transient response
Modern converters with COT control also create a ripple voltage by
sensing the current in the low-side MOSFET. The COT control then
adds this voltage to the internal feedback voltage or to the internal
voltage reference
POWER ELECTRONICS
AC voltage controllers, current control and applications
Constant on-time (COT) hysteretic converter keeps the frequency as
constant as possible
POWER ELECTRONICS
AC voltage controllers, current control and applications
POWER ELECTRONICS
AC voltage controllers, current control and applications
POWER ELECTRONICS
AC voltage controllers, current control and applications
POWER ELECTRONICS
AC voltage controllers, current control and applications
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
POWER ELECTRONICS
AC voltage controllers, current control and applications
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
There are modern synchronous step-down converters that employ a
minimum on-time control in a hysteretic PWM control scheme. The
hysteretic comparator is still used. Operation of this control scheme is
quite simple. When the output voltage is below the regulation
threshold, the error comparator begins a switching cycle by turning
on the high-side switch. This switch remains on until the minimum
on-time expires and either the output voltage is above the regulation
threshold or the inductor current is above the current-limit threshold.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
Once off, the high-side switch remains off until the minimum offtime expires and the output voltage again falls below the
regulation threshold. During the off period, the low-side
synchronous rectifier turns on and remains on until either the
high-side switch turns on again or the inductor current
approaches zero. To help improve efficiency, an internal
synchronous rectifier eliminates the need for an external
Schottky diode,
POWER ELECTRONICS
AC voltage controllers, current control and applications
Current control and applications:
Hysteretic PWM control in the MAX8640Y/MAX8640Z step-down converter
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294
POWER ELECTRONICS
Prasanna Kumar C
Department of Electrical and
Electronics Engineering
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Power electronics can play a vital role in improving the reliability
and security of the nation’s electric grid. The following benefits can
be realized: i) Increased loading and more effective use of
transmission corridors ii) Added power flow control iii) Improved
power system stability iv) Increased system security v) Increased
system reliability vi)
Added flexibility in siting new generation
facilities vii) Elimination or deferral of the need for new
transmission lines
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Thyristor Controlled Reactor:
In a TCR a reactor is connected in series to two
opposite poled thyristors. One of these
thyristors conducts in each half cycle of supply
frequency. The gating signal to each thyristor is
delayed by an angle α (often called the firing
or conduction angle) from the zero crossing of
the source voltage
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Typical SVC Scheme:
Static Var Compensator
TCR = thyristor-controlled reactor
TSR = thyristor-switched reactor
TSC = thyristor-switched capacitor
MSC = mechanically-switched capacitor
MSR = mechanically-switched reactor
FC = fixed capacitor
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Typical SVC Scheme:
The SVC uses the conventional thyristor to achieve fast control of shunt
connected capacitors and reactors. The SVC provides a rapid and fine
control of voltage without moving parts
The TCR portion of SVC consists of anti-parallel thyristors in series with
shunt reactors usually in a delta configuration
These thyristors may be switched at any point over the half wave (90 to
180 electrical degrees behind the voltage wave) to provide a fully
adjustable control from 100 % to zero reactive power absorption
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Synchronous Voltage Source (SVS)
Harmonic currents are generated at any
angle other than 90 (full conduction) and
180 (zero conduction).
High-power electronic devices will play an important role in
improving grid reliability, including use in energy storage
systems, FACTS applications, distributed energy (DE), and
HVDC.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
STATCOM (synchronous static compensator)
consists of a SVS that is supplied by a dc
storage capacitor Cdc.
The SVS is connected in shunt with the ac
system bus through a coupling transformer
with a leakage reactance of XT.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems and drives:
• However pure reactive injection or absorption is neither
possible nor desirable
• Since the converter is supplied by a dc capacitor, the voltage
across the capacitor will fall if the STATCOM is not lossless
• The dc capacitor voltage can be regulated by replenishing the
losses due to switching and in the coupling transformer circuit
by drawing power from the ac system
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems and drives:
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
The advantages of HVDC are in conversion:
• Availability of high power semiconductor devices
• Decentralized renewable energy generation sources
• Increased power transfer with existing transmission system
• Effective control of power flow needed in a deregulated
environment
• Norms for Power quality
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
The advantages of HVDC are in conversion(cont.):
• High switching speeds and low losses
• Ease of controlling of bulk power
• Robust components and high reliability
• Low power consumption during operation
• Ensure efficient and safe power handling
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
The disadvantages of HVDC are in conversion:
Higher losses in static inverters at smaller transmission distances
The cost of the inverters may not be offset by reductions in line
construction cost and lower line loss.
High voltage DC circuit breakers are difficult to build because some
mechanism must be included in the circuit breaker to force current
to zero, otherwise arcing and contact wear would be too great to
allow reliable switching
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
The disadvantages of HVDC are in conversion:
Expensive inverters with limited overload capacity
The cost of transmission per kilometer is reduced by using the lines
of fairly of large distances
Provision of special protection to switching devices & filtering
elements
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Flexible AC Transmission System(FACTS):
Flexible AC Transmission System (FACTS) is a integrated concept
based on power electronic switching converters and dynamic
controllers to enhance the system utilization and power transfer
capacity as well as the stability, security, reliability and power
quality of AC system interconnections.
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Flexible AC Transmission System(FACTS):
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
Flexible AC Transmission System(FACTS):
• Better utilization of existing transmitting system assets
• Increased transmission reliability and availability
• Increased dynamic and transient grid
• Stability and reduction of loop flows
• Increased quality of supply for sensitive industries
• Environmental benefits
POWER ELECTRONICS
AC voltage controllers, current control and applications
Power electronic applications in power systems:
POWER ELECTRONICS
AC voltage controllers, current control and applications
POWER ELECTRONICS
AC voltage controllers, current control and applications
STATIC VAR COMPENSATOR
Regulate the voltage and stabilize(dynamic) the system SVC is an
automated impedance matching device, designed to bring the
system closer to unity power factor
If load is capacitive (leading), the SVC will use reactors
Under inductive (lagging) ,the capacitor banks are automatically
switched in
SVR may be placed near high and rapidly varying loads, such as arc
furnaces, where they can smooth flicker voltage
POWER ELECTRONICS
AC voltage controllers, current control and applications
STATIC VAR COMPENSATOR
POWER ELECTRONICS
AC voltage controllers, current control and applications
Applications Of FACTS:
• Steady state voltage stability
• Power flow control
• Damping of power system oscillations
• Reducing generation costs
• HVDC link application
• Deregulated power systems
• Interconnection of renewable, distributed generation and
storages
THANK YOU
Prasanna Kumar C
Department of Electrical and Electronics
prasannak@pes.edu
+91 80 9880676575 Extn 294