EE0314- POWER ELECTRONICS LAB
REFERENCE MANUAL
SEMESTER VI
DEPARTMENT OF ELECTRICAL AND ELECTRONICS
ENGINEERING
SRM UNIVERSITY
KATTANKULATHUR-603203
1
EXPT. NO. 1 :
Pre lab Questions
Single Phase Half Converter
1.
What is the delay angle control of converters?
2. What is natural or line commutation?
3. What is the principle of phase control?
4. What is extinction angle?
5. Can a freewheeling diode be used in this circuit and justify the reason?
2
SINGLE PHASE HALF CONTROLLED BRIDGE RECTIFIER
Aim:
To study the operation of single phase half controlled converter using R and RL load and to
observe the output waveforms.
Apparatus required:
1.
Power thyristors
2.
Rheostat
3.
CRO
4.
Transformer (1-phase) 230V/24V
5.
Connection wires
Single Phase Half Controlled Bridge Rectifier:
Circuit Diagram
3
Model Graph:
Observation Table:
Serial
No.
Triggering angle
‘α’ degree
Output voltage
Vo
(volt)
(measured)
Time period(ms)
1
2
3
Procedure:
1.
Make the connections as per the circuit diagram.
2.
Connect CRO and voltmeter across the load.
3.
Keep the potentiometer at the minimum position.
4.
Switch on the step down ac source.
5.
Check the gate pulses at G1-K1 & G2-K2, respectively.
6.
Observe the wave form on CRO and note the triggering angle ‘α’ and
7.
Note the corresponding reading of the voltmeter. Also note the value of Maximum amplitude Vm
from the waveform.
4
8.
Set the potentiometer at different positions and follow the step given in (6) for every position.
9.
Tabulate the readings in the observation column.
Theory:
A semi converter uses two diodes and two thyristors and there is a limited control over the level of dc
output voltage. A semi converter is one quadrant converter. A one-quadrant converter has same polarity
of dc output voltage and current at its output terminals and it is always positive. It is also known as twopulse converter. Figure shows half controlled rectifier with R load. This circuit consists of two SCRs T1
and T2, two diodes D1 and D2. During the positive half cycle of the ac supply, SCR T1 and diode D2 are
forward biased when the SCR T1 is triggered at a firing angle ωt = α, the SCR T1 and diode D2 comes to
the on state. Now the load current flows through the path L - T1- R load –D2 - N. During this period, we
output voltage and current are positive. At ωt = π, the load voltage and load current reaches to zero, then
SCR T1 and diode D2 comes to off state since supply voltage has been reversed. During the negative half
cycle of the ac supply, SCR T2 and diode D1 are forward biased. When SCR T2 is triggered at a firing
angle ωt = π + α, the SCR T2 and diode D1 comes to on state. Now the load current flows through the
path N - T2- R load – D1 -L. During this period, output voltage and output current will be positive. At ωt
= 2π, the load voltage and load current reaches to zero then SCR T2 and diode D1 comes to off state since
the voltage has been reversed. During the period (π + α to 2π) SCR T2 and diode D1 are conducting.
Vout=(√2Vs)(1+Cosα)/π
Result:
Thus the operation of single phase half controlled converter using R and RL load has studied and the
output waveforms has been observed.
5
Post lab Questions:
Single Phase Half Converter
1. What is conduction angle?
2. What are the effects of adding freewheeling diode in this circuit?
3. What are the effects of removing the freewheeling diode in single phase semi converter?
4. Why is the power factor of semi converters better than that of full converters?
5. What is the inversion mode of converters?
6
EXPT. NO. 2:
Pre lab Questions:
Single Phase Full Converter:
1. State the type of commutation used in this circuit?
2. What will happen if the firing angle is greater than 90 degrees?
3. What are the performance parameters of rectifier?.
4. What are the advantages of three phase rectifier over a single phase rectifier?
5. What is the difference between half wave and full wave rectifier?
7
SINGLE PHASE FULLY CONTROLLED CONVERTER
Aim:
To study the operation of single phase fully controlled converter using R and RL load and to
observe the output waveforms.
Apparatus Required:
1.
Power thyristors
2.
Rheostat
3.
CRO
4.
Transformer (1-phase) 230V/24V
5.
Connection wires
Circuit Diagram
8
Model Graph:
Observation Table:
Serial
No.
Triggering angle
‘α’ degree
Output voltage
Voav
(volt)
(measured)
1
2
3
Procedure:
1.
Single Phase Fully Controlled Bridge Rectifier
2.
Make the connections as per the circuit diagram.
3.
Connect CRO and multimeter (in dc) across the load .
9
Time period(ms)
4.
Keep the potentiometer (Ramp control) at the minimum position (maximum resistance).
5.
Switch on the step down ac source.
6.
Check the gate pulses at G1-K1, G2-K2,G3-K3,& G4-K4 respectively.
7.
Observe the waveform on CRO and note the triggering angle ‘α’ and note the corresponding
reading of the multimeter. Also note the value of maximum amplitude Vm from the waveform.
8.
Set the potentiometer at different positions and follow the step given in (6) for every position.
9.
Tabulate the readings in observation column.
10.
Draw the waveforms observed on CRO.
Theory:
A fully controlled converter or full converter uses thyristors only and there is a wider control over
the level of dc output voltage. With pure resistive load, it is single quadrant converter. Here, both the
output voltage and output current are positive. With RL- load it becomes a two-quadrant converter. Here,
output voltage is either positive or negative but output current is always positive. Figure shows the
quadrant operation of fully controlled bridge rectifier with R-load.
Fig shows single phase fully
controlled rectifier with resistive load. This type of full wave rectifier circuit consists of four SCRs.
During the positive half cycle, SCRs T1 and T2 are forward biased. At ωt = α, SCRs T1 and T3 are
triggered, then the current flows through the L – T1- R load – T3 – N. At ωt = π, supply voltage falls to
zero and the current also goes to zero. Hence SCRs T1 and T3 turned off. During negative half cycle (π
to 2π).
SCRs T3 and T4 forward biased. At ωt = π + α, SCRs T2 and T4 are triggered, then current flows through
the path N – T2 – R load- T4 – L. At ωt = 2π, supply voltage and current goes to zero, SCRs T2 and T4
are turned off. The Fig-3, shows the current and voltage waveforms for this circuit. For large power dc
loads, 3-phase ac to dc converters are commonly used. The various types of three-phase phase-controlled
converters are 3 phase half-wave converter, 3-phase semi converter, 3-phase full controlled and 3-phase
dual converter. Three-phase half-wave converter is rarely used in industry because it introduces dc
component in the supply current. Semi converters and full converters are quite common in industrial
applications. A dual is used only when reversible dc drives with power ratings of several MW are
required. The advantages of three phase converters over single-phase converters are as under: In 3-phase
10
converters, the ripple frequency of the converter output voltage is higher than in single-phase converter.
Consequently, the filtering requirements for smoothing out the load current are less. The load current is
mostly continuous in 3-phase converters. The load performance, when 3- phase converters are used, is
therefore superior as compared to when single-phase converters are used.
Vout=(2Vs)(Cosα)/π
Iavg=Vavg/R
Result:
Thus the operation of single phase fully controlled converter using R and RL load has been
studied and the output waveforms has been observed.
11
Post lab questions
Single phase full converter
1. If firing angle is greater than 90 degrees, the inverter circuit formed is called as?
2. What is displacement factor?
3. What is Dc output voltage of single phase full wave controller?
4. What are the effects of source inductance on the output voltage of a rectifier?
5. What is commutation angle of a rectifier?
6. What are the advantages of three phase rectifier over a single phase rectifier?
12
EXPT. NO: 3
Pre lab questions
Single phase AC voltage controller using TRIAC
1. Why should the two trigger sources be isolated?
2. What are the advantages and the disadvantages of phase control?
3. What is phase control?
4. What are the advantages of bidirectional controllers?
5. What is meant by duty cycle in ON-OFF control method?
13
1-PHASE AC VOLTAGE CONTROL USING TRIAC
Aim:
To study the 1-phase AC voltage control using TRIAC.
Apparatus Required:
i)
Lamp – 60W
ii)
Resistor - 100 / 1W
iii)
Potentio meter – 100K
iv)
Capacitor – 0.1F / 400V
v)
Resistor – 1K
vi)
DIAC – DB3
vii)
TRIAC BT 136
viii)
Unearthed oscilloscope
Circuit Diagram
Circuit Operation:
1.
When potentiometer is in minimum position drop across potentiometer is zero and hence
maximum voltage is available across capacitor. This Vc shorts the diac (Vc > Vbo) and triggers
the triac turning triac to ON – state there lamp glows with maximum intensity.
14
2.
When the potentiometer is in maximum position voltage drop across potentiometer is
maximum. Hence minimum voltage is available across capacitor (Vc M Vbo) hence triac to is
not triggered hence lamp doesnot glow.
3.
When potentiometer is in medium position a small voltage is available across capacitor hence
lamp glows with minimum intensity.
Tabular Column:
S.No.
Firing Angle(α)
Output Voltage(Volts)
Time period(ms)
1
2
3
Procedure:
1.
Connections are given as per the circuit diagram
2.
Initially potentiometer kept at minimum position so lap does not glow at this instant.
3.
Note the voltage across the diac and triac.
4.
Capacitor and potentiometer using multimeter and CRO.
5.
Potentiometer is now placed at medium and then to minimum position and their voltages were
noted.
Theory:
Triac is a bidirectional thyristor with three terminals. Triac is the word derived by combining the capital
letters from the words TRIode and AC. In operation triac is equivalent to two SCRs connected in antiparallel. It is used extensively for the control of power in ac circuit as it can conduct in both the direction.
Its three terminals are MT1 (main terminal 1), MT2 (main terminal 2) and G (gate).
15
Result:
Thus the operation and performance of the 1-phase AC voltage control using DIAC and TRIAC.
16
Post lab questions
Single Phase AC voltage controller using TRIAC
1. What type of commutation is used in this circuit?
2. What are the effects of load inductance on the performance of AC voltage controllers?
3. What is extinction angle?
4. What are the disadvantages of unidirectional controllers?
5. What are the advantages of ON-OFF control?
17
EXPT. NO. 4:
Prelab questions
Modified Mc Murray Full bridge Inverter
1. What is the difference between Mcmurray half bridge and full bridge inverter?
2. What is meant by Mcmurray inverter?
3. What is the type of commutation used in this circuit?
4. What is the other name for this inverter circuit?
5. Advantages of Mc Murray inveter?
18
MODIFIED MC-MURRAY – BEDFORD FULL BRIDGE INVERTER
Aim:
To study the operation of a modified Mc-Murray Bedford full bridge inverter.
Apparatus Required:
i)
Modified Mc-Murray Bedford inverter kit
ii)
Connecting wires
iii)
CRO and probes
Circuit Diagram
19
Model Graph
Tabular Column:
S.No
Frequency
Voltage Amplitude(V)
Time
period(ms)
1
Minimum
2
Maximum
Procedure:
i)
Connections are made as per the circuit diagram
ii)
Power supply is switched ‘ON’ and the output waveforms are noted.
Theory:
The power circuit diagrams of a modified Mc-Murray Bedford half and full bridge inverter is
shown in the figure.
20
A half bridge modified Mc-Murray Bedford inverter uses lesser number of thyristors and diodes as
compared with the full bridge one.
The inverter consists of main thyristors T1,T2 and feedback diodes D1, D2 commutation circuitry
consists of two capacitors C1, C2 and magnetically coupled inductors L1 and L2 constitute one inductor
with a center rapped so that L1 = L2 = L. The inductance of the order 50H. The inductor is wound on a
core with an air gap so as to avoid saturation. The value of the capacitance for the two capacitors is the
same (C1=C2=C). It is a voltage commutated VSI.
In a branch consisting of two tightly coupled inductors in series with two thyristors if the
thyristors is turned on, then the other thyristor is turned off automatically. This type of commutation is
called complementary commutation.
21
Result:
Thus the operation of a modified Mc-Murray Bedford full bridge inverter is studied and the
waveforms are drawn.
22
EXPT. NO. 5:
Pre lab Questions
Single Phase parallel Inverter
1. What is parallel inverter? Why is it called so?
2. What is the purpose of capacitor in the parallel inverter?
3. What is the purpose of transformer in the parallel inverter?
4. IS the parallel inverter naturally commutated or force commutated?
5. What are the advantages of parallel resonant inverters?
23
PARALLEL INVERTER
Aim:
To study the operation of parallel inverter.
Apparatus Required:
i)
Parallel inverter kit
ii)
Inductor
iii)
Transformer
iv)
CRO
This module consists of two units – (1) Firing circuit and 92) Power circuit.
Circuit Diagram
24
Model Graph
Tabular Column:
S.No.
Frequency
1
Minimum
2
Maximum
Voltage Amplitude(V)
Time period(ms)
Procedure:
1.
Switch on the firing circuit.
Observe the trigger outputs TP and TN by varying frequency
potentiometer and by operating ON/OFF switch.
2.
Then connect input DC supply to the power circuit. Connect trigger outputs to Gate and Cathode
of SCR TP & TN.
3.
Apply trigger pulses to SCR
4.
Observe voltage waveforms across load. Output voltage is square wave only.
5.
Vary the load, vary the frequency and observe waveforms.
25
Theory:
The circuit is a typical class C Parallel inverter. Assume TN to be ON and TP to be OFF. The
bottom of the commutating capacitor is charged to twice the supply voltage and remains at this value until
TP is turned on. When TP is turned on, the current flows through lower half of the primary TP and
commutating inductance L. Since voltage across C cannot instantaneously, the common SCR cathode
point rises approximately to 2V dc and reverses bias TN Thus TN turns off and C discharges through L, the
supply circuit and then recharges in the reverse direction. The autotransformer action makes C to charge
making now its upper point to reach +2V dc volts ready to commutate Tp, When TN is again turned on
and the cycle repeats.
Free wheeling diodes Dp and DN assist the inverter in handling a wide range of loads and the value
of C may be reduced since the capacitor now does not have to carry the reactive current. To dampen the
feedback diode currents within the half period, feedback diodes are connected to tapping of the
transformer at 25V tapping.
(1) Firing Circuit:
This unit generates two pairs of pulse transformer isolated trigger pulses to trigger two SCR’s
connected in center tapped transformer type parallel inverter. Frequency of the inverter can be varied
from 75Hz to 200 Hz approximately.
(2) Power Circuit:
This unit consists of two SCR’s, two free wheeling diodes, commutation inductor, commutation
capacitor and a center tapped transformer to be inter connected to make parallel inverter. All the points
are brought out to the front panel. A switch and fuse is provided for input DC supply. All the devices are
mounted on proper heat sink. Each device is protected by snubber circuit.
Front Panel Details:
1.
Frequency
:
Potentiometer to vary the inverter frequency from 75Hz
to 200 Hz approximately.
2.
ON / OFF
:
Switch for trigger outputs
3.
T1 & T2
:
Trigger outputs
4.
Power
:
Mains switch for firing circuit
5.
Vdc in
:
Terminals for DC input from 30V/2A RPS unit
26
6.
ON
:
Switch for DC input
7.
Tp & Tn
:
SCR’s 10A/600V
8.
Dp & Dn
:
Diodes 10A/600V
9.
L
:
Inductance - 300H/2A
10.
C
:
6.8F/100V
11.
Load
:
Terminals to connect load.
12.
O
:
Transformer center tap point which should be
connected to positive of DC supply after fuse.
13.
Fuse
:
14.
Output Transformer :
2A Glass fuse.
Primary – 30V-25V-025V – 30V
Secondary – 0-30V/2Amps.
27
Result:
Thus the operation of a parallel inverter is studied and the output waveforms are measured and
drawn.
28
Post lab questions
Single phase parallel Inverter
1. What is the purpose of the inductor in the parallel inverter?
2. During its operation, capacitor voltage reaches 2Vs. How?
3. What is the significance of the split phase transformer?
4. During operation, what is the voltage across primary winding of the transformer?
5. Capacitor current flows in how many modes of the operation of parallel inverter?
29
EXPT.NO 6:
Pre Lab questions
R, R-C AND UJT TRIGGERING CIRCUITS
1. UJT triggering circuit is also known as?
2. Types of triggering circuit?
3. What is the purpose of series resistor?
4. What is the condition for triggering the circuit?
5. What is the function of pulse transformer in firing circuit?
30
R, R-C AND UJT TRIGGERING CIRCUITS
Aim:
To study the operation of resistance, resistance capacitance and UJT triggering circuits of SCR
Circuit Diagram: R – Triggering Circuit:
31
Model Graph: R – Triggering Circuit:
Tabular Column
S.No.
Input
Voltage
(V)
Input
Cycle
Time
(Ms)
Voltage
across
Resistor(V)
1
Procedure
R Firing
1.
Connections are made as shown in fig.
2.
Switch on the power supply to the CRO.
3.
Set the CRO to the line trigger mode.
4.
Switch on power supply to the SCR trainer.
32
Voltage
across
zener
diode
(V)
Voltage
across
capacitor
(V)
Voltage
across
load
(V)
5.
Observe the waveform on the CRO.
6.
Study the waveforms for various firing angle by varying the pot in R trigger circuit.
7.
Observe the range of firing angle control.
8.
For any one particular firing angle plot the waveforms of the ac voltage, voltage across the load
and the SCR.
9.
Measure the average dc voltage across the load and rms value of the ac input voltage using a
digital multimeter.
10.
Calculate the dc output voltage using the equation.
V
- Vrms value of ac input voltage
Vm - \/2Vrms.And compare the measured value.
Theory:
Resistance Triggering:
Resistance trigger circuits are the simplest & most economical method. During the positive half cycle of
the input voltage, SCR become forward biased but it will not conduct until its gate current exceeds Igmin
. Diode D allows the flow of current during positive half cycle only. R2 is the variable resistance & R is
the stabilizing resistance .R1 is used to limit the gate current. During the positive half cycle current Ig
flows. Ig increases and when Ig= Igmin the SCR turns ON .The firing angle can be varied from 0 — 90°
by varying the resistance R.
33
Circuit Diagram: RC Triggering Circuit:
Model Graph:
34
Tabular Column:
S.No.
Input
Voltage
(V)
Input
Cycle
Time
(Ms)
Resistance
Value
(K _ )
O/P
Voltage
V rms (V)
Voltage
Across
(AnodeCathode)
V rms (V)
Procedure:
RC FIRING:
1.
Connections are made as shown in fig.
2.
Switch on the power supply to the CRO .
3.
Set the CRO to the line trigger mode.
4.
Switch on power supply to the SCR trainer.
5.
Observe the waveform on the CRO.
6.
Study the waveforms for various firing angle by varying the pot in R trigger circuit.
7.
Observe the range of firing angle control. t u t e o f T e c h n o l o g y Page 53
8.
For any one particular firing angle plot the waveforms of the ac voltage, voltage across the load
and the SCR.
9.
Measure the average dc voltage across the load and rms value of the ac input voltage using g' a
digital millimeter.
10.
Calculate the dc output voltage using the equation.
35
Theory:
R —C Triggering:
By varying the variable resistance R, the firing angle can be varied from 0 —180° .In the negative
half cycle the capacitance C charges through the diode D2 with lower plate positive to, the peak supply
voltage Emax .This Capacitor voltage remains constant at until supply voltage attains zero value. During
the positive half cycle of the input voltage, C begins to charge through R. When the capacitor voltage
reaches the minimum gate trigger voltage SCR will turn on.
Circuit Diagram: UJT Triggering Circuit
36
Model Graph:
Tabular Column:
Resistor
value(r)
(ω)
Capacitor
voltage
Vc
Charging
time
(ms)
Discharging
Time
(ms)
Voltage vo
(v)
Time
Period
(ms)
Procedure:
1.
Connect a & k terminal of UJT triggering circuit to the gate cathode terminals of SCR.
2.
Give a 24 V ac supply.
3.
Observe the waveforms and plot it for one particular firing angle by adjusting the potentiometer
37
and observe the range over which firing angle is controllable.
4.
Observe that capacitor voltage is set at every half cycle.
Theory:
A synchronized UJT triggered circuit using an UJT is shown in the figure. Diodes ‘D1’ to ‘D4’
rectify ac to dc. Resistor R1 lowers Vdc to a suitable value for the zener diode and UJT. Zener diode ‘Z’
functions to clip the rectified voltage to a standard level, ‘Vz’ which remains constant except near the Vdc
zero. The voltage Vz is applied to the charging circuit RC. Current ‘I’, charges capacitor ‘c’ at a rate
determined by ‘R’ voltage across capacitor is marked by ‘Vc’ as shown. When ‘Vc’ reaches the
unijunction threshold voltage Vz, the t-B1 junction of UJT breaks down and the capacitor ‘c’ discharges
through the primary of pulse transformer sending a current ‘C2’ as shown.
As the current ‘i2’ is in the form of pulse, windings of the pulse transformer have pulse voltages at
their secondary terminals. Pulse at the two secondary windings feeds the same in phase pulse to two
SCRs of a full wave circuits. SCR with positive anode voltage would turn ON. As soon as the capacitor
discharges, it starts to recharge as shown. Rate of rise of capacitor voltage can be controlled by varying
‘R’. The firing angle can be controlled up to above 150o. This method of controlling the output power
by varying the charging resistor ‘r’ is called ramp control, open loop control (or) manual control.
38
Result:
Thus the operation of resistance, resistance capacitance and UJT triggering circuits of SCR has
been studied.
39
Post lab questions
R, R-C AND UJT TRIGGERING CIRCUITS
1. Explain how synchronization of the triggering circuit with the supply voltage across SCR is achieved?
2. How can the capacitor charging be controlled?
3. What is the maximum value of firing angle which can be obtained from the circuit?
4. How is the output power to the triggering circuit controlled?
5. Compare UJT triggering circuit with RC firing circuit?
40
EXPT. NO. 7:
Pre lab questions
SERIES INVERTER
1. Why is this circuit called as series inverter?
2. What is the type of commutation for series inverter?
3. What is the configuration of inductor?
4. What is the principle of series inverter?
5. Disadvantages of series inverter?
41
SERIES INVERTER
Aim:
To study the operation of series inverter and to obtain variable AC from DC input.\
Apparatus Required:
i)
Series inverter module
ii)
Loading rheostat - 50
iii)
CRO
iv)
Connection wire
This unit consists of power circuit and firing circuit sufficient to build and study the modified
series inverter.
Circuit Diagram
42
Model Graph:
t u t e o f T e c h n o l o g y Page 56
Observation Table:
A
S. No
Amplitude (volt)
Ton (ms)
1
2
43
Toff (ms)
Procedure o l o g y Page 58
1.
To begin with switch on the power supply to the firing circuit check that Trigger pulses by varying
the frequency.
2.
Connections are made as shown in the circuit diagram.
3.
Now connect trigger outputs from the firing circuits to gate and cathode of SCRs T1 & T2.
4.
Connect DC input from a 30v/2A regulated power supply and switch on the input DC
supply.
5.
Now apply trigger pulses to SCRs and observe voltage waveform across the load.
6.
Measure Vrms & frequency of o/p voltage waveform.
Firing Circuit: This part generates two pairs of pulse transformer isolated trigger two SCR’s connected
as series inverter. ON/OFF switch is provided for the trigger pulses which can be used to switch ON the
inverter. Frequency of the inverter can be varied from 100 Hz to 1 KHz approximately.
Power Circuit: This part consists of two SCR’s two diodes. A center tapped inductor with tappings and
4 capacitors. Input supply terminals with ON/OFF switch and a fuse is provided. All the devices in this
unit mounted on a proper heat sink, snubber circuit for dv/dt protection and a fuse in series with each
device for short circuit protection.
All the points are brought out to front panel for inter connections. They have to be interconnected
as shown in the circuit diagram. Fly wheeling diodes can be connected across SCR’s and its effect can be
observed.
Theory:
This circuit which converts DC power into AC power is called inverter.
If the thyristor
commutation circuit of the inverter is in series with the Load, then the inverter is called “Series are tightly
coupled. In this circuit, it is possible to turn-on-thyristor Tp before the current through thyristor Tn has
become zero and vice-versa.
Therefore, the Modifed Series Inverter can be operated behond the
resonance frequency (fr) of the circuit. Inverter is operated at the resonance frequency (fr) if the load
current waveform has low frequency and should not have zero current interval. The inverter’s resonance
frequency depends on the values of L, R and C in the circuit.
44
Front Panel Details:
1.
Frequency
:
Potentiometer to vary the inverter frequency.
From 100 Hz to 1 KHz approximately.
2.
Gate, Cat
:
Trigger outputs to connect to Gate and
Cathode of SCR
3.
ON / OFF
:
Switch for trigger outputs
4.
T1 and T2
:
Trigger outputs
5.
Power
:
Mains switch for firing circuit
6.
Vdc in
:
Terminals for DC input 30V/2A max from
RPS
7.
ON / OFF
:
Switch for DC input
8.
Fuse
:
Fuse for dc input-2 Amps Glass Fuse
9.
T1 and T2
:
SCR’s TY 616.12A / 600V
10.
D1 and D2
:
Diodes BYQ28. 4A/200V
11.
L2, L1, Lm, L1, L2
:
10mH – 5mH – 0 – 5mH – 10mH/2 Amps
12.
C1 and C1
:
6.8  farad / 100V
13.
C2 and C2
:
10  farad / 100V
45
Result:
Thus the operation of a series inverter is studied.
46
Post lab questions
SERIES INVERTER
1. What is the dead zone of an inverter?
2. Up to what maximum voltage will the capacitor charge during circuit operation?
3. What is the amount of power delivered by capacitor?
4. What is the purpose of coupled inductors in half bridge resonant inverters?
5. Types of resonant pulse inverters?
47
EXPT. NO.8:
Pre lab questions
SPEED CONTROL OF DC MOTOR
1. What type of commutation is applied to Jones Chopper?
2. Give the commutating element to form the commutating circuit for the main thyristor?
3. Give the reason for the high efficiency of this chopper.
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SPEED CONTROL OF DC MOTOR
USING – 1-PHASE HALF CONTROLLED RECTIFIER
Aim:
To study the speed control of a dc motor by varying armature applied voltage through phase
controlled converter.
Apparatus Required:
i)
DC motor control unit
ii)
DC ammeter
iii)
DC voltmeter
iv)
CRO
v)
DC motor
Circuit Diagram
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DC Motor Speed Control Unit (Power Circuit) 230V/5A
This power circuit consists of two SCR’s and three diodes. These devices can use to built single
phase half wave converter, single phase full wave converter and single phase half controlled bridge
converter, and also single phase AC voltage controller power circuits.
Each device in the unit is mounted on an appropriate heat sink and is protected by snubber circuit.
Short circuit protection is achieved using glass fuses. A circuit breaker is provided in series with the input
supply for over load protection and to switch ON/OFF the supply to the power circuit.
The Gate and Cathode of each SCR’s brought out on the front panel for firing pulse connection. A
digital voltmeter and an ammeter is mounted on the front panel to measure the armature voltage and
current. All devices schematic is printed on the front panel.
Specifications:
Input
:
10V to 230V single phase
SCR
:
(V) rrm 1200V, (I) av : 10 amps, 25TTS12
International rectifier make.
Power diodes & Free
Wheeling diode
:
(V) rrm : 1200V, (I) 16 amps, 12KLR 16DS
Fuses
:
6 Amps Glass fuses
MCB
:
Two pole 6 amps / 230V
Heat Sink
:
PI-46, 50mm
Snubber
:
R-250 Ohms / 5 Watts c-0.1 Microfarad / 1000V
:
Terminals to connect 1-phase AC input from single phase
Front Panel Details:
AC Input
isolation transformer.
Output
:
Terminals after the MCB to be connected to power circuit
Digital voltmeter
:
3 ½ digit voltmeter to measure output voltage
Digital ammeter
:
3 ½ digital ammeter to measure output voltage
Circuit Breaker
:
6 Amps, AC power ON/OFF to the circuit and for protection
T1, T2
:
Trigger pulse connections from the firing circuit
D2, D4
:
Power diodes
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Dm
:
Free wheeling diode
Field (+and-)
:
Field supply for DC motor for motor control experiments.
(With indicator)
Back Panel Details:
3 pin mains socket for AC mains supply to field supply bridge rectifier Glass fuse holders for 6
fuses in series with each SCR’s.
Procedure:
Switch ON the mains supply to the single phase converter firing circuit. Observe the test points
and trigger outputs.
Verify the trigger outputs and their phase sequence.
Vary the firing angle
potentiometer and observe the trigger outputs. The pulse train width will increase as we decrease the
firing angle from 180o to 0o. It is 0 o to 180o and 50% at 90o soft start and stop feature is provided for
trigger outputs. When we press of ON/OFF switch the trigger outputs will start at 180 o and slowly
increased to the firing angle set by firing angle potentiometer. The acceleration time is set in the factor
(10 seconds).
When we release the ON/OFF switch the trigger outputs will slowly decreased to 180 o from the
set firing angle. The deceleration time is set in the factory.(-2 seconds)
The deceleration time is very short compared to acceleration time. Make sure that all the trigger
outputs are proper before connecting to the power circuits. Make the connections in the power circuit as
given in the circuit through isolation transformer. Initially keep the input supply at low voltage say 30
volts. Connect the trigger outputs from firing circuit to the corresponding SCR’s Gate and Cathode.
Initially connect a Rheostat of 50 Ohms / 5amps. Switch ON the trigger outputs observe the voltage
waveforms across load by varying the firing angle potentiometer. Compare with the expected waveforms,
if the unit is working properly switch OFF the trigger outputs and switch OFF the MCB. Connect field
terminals of DC motor to the field supply points in the power circuit. The connect armature terminal of
the DC motor through the rheostat and the rheostat and the ammeter provided in the unit to the output of
rectifier. Switch ON the field supply. Set the field voltage to some value – 150Volts. This voltage can
be measured using the voltmeter provided in the rectifier. Set the input voltage to 100Volts. Initially
keep the firing angle pot at 180o. Initially keep the resistance at maximum position and cut off once the
DC motor starts. This is to limit the starting current. Switch On the MCB and trigger outputs. Vary the
firing angle potentiometer and note down the output voltage, output current and measure the speed of the
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DC motor for different values of firing angle. Note down these values in the tabular column. And also
observe the voltage waveforms. We can observe that back emf will increase as the speed increases. Next
vary the input voltage upto 230 volts in steps and note down the readings in the tabular column.
Armature Control:
S.No.
Output
Voltage(V)
Duty Cycle(%)
1
2
3
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Frequency
Speed(RPM)
Current
Result:
Thus the speed control of DC motor is performed by varying armature voltage through phase
controlled converter
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Post lab questions
SPEED CONTROL OF DC MOTOR
1. How the load current is smooth other than pulsating?
2. The inductance L maintains the load current to diodes D when SCR T is not conducting. Hence, the motor
torque and load current is smooth rather than pulsating.
3. What is the commutating voltage across capacitor C?
4. Give the torque equation for speed control of DC machine.
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EXPT. NO. 9:
Pre lab questions
SPEED CONTROL OF UNIVERSAL MOTOR:
1. What is universal motor?
2. How speed is controlled by using a thyristor?
3. What is delay angle?
4. What is duty cycle?
5. What is meant by controlled rectifier?
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SPEED CONTROL OF UNIVERSAL MOTOR
Aim:
To study the speed control of a Universal motor by varying armature applied voltage through phase
controlled converter.
Apparatus Required:
i)
Universal kit
ii)
CRO
iii)
Batch cards motor
iv)
Universal motor
This unit consists of two parts:
(a) Firing circuit and (b) Power circuit
Speed Control of Universal Motor Using AC Voltage Control
Circuit Diagram:
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Speed control of DC motor using Single phase Half wave converter
Speed control of DC motor using Single phase full wave converter
Single phase Half controlled bridge rectifier
Tabular Column:
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Sl.
No.
Input Voltage
Vin
Firing Angle
Output
Voltage – V0
Output
Current I0
Speed
RPM
a) Firing Circuit:
This unit, generates line synchronized 2 pulse transformer isolated trigger pulses. These trigger
pulses can be used to trigger.
(i)
Single phase AC phase control using SCR’s (Antiparallel SCR’s)
(ii)
Single phase AC phase control using triac.
(iii)
Single phase Half wave rectifier (single SCR)
(iv)
Single phase Full wave rectifier (Two SCR’s)
(v)
Single phase Half controlled bridge rectifier (Two SCR’s & Two diodes) power circuits.
The firing circuit is based on zero crossing detector, ramp generator, op-amp comparator and amplifier
/ pulse transformer isolation method.
Front Panel Details:
1.
Power
:
Mains switch for firing circuit with built in indicator
2.
Firing angle
:
Potentiometer to vary the firing angle from 180o to 0o
3.
SCR / Triac
:
Selection switch for trigger O/P 1 for SCR/Triac
4.
OFF/ON
:
Switch for trigger O/Ps with soft start feature.
5.
Trigger O/Ps
:
T1 / TR
:
T2
:
Trigger O/P for SCR2
Power Circuit:
The power circuit consists of 2 SCR’s, 3 diodes and a Triac. The power devices are mounted on
suitable heat sink for power dissipation. The snubber circuit is connected for dv/dt protection. A fuse is
also provided in series with the devices for short circuit or over current protection. In the input side a
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MCB is provided to switch ON/OFF the supply to the power circuit.
A voltmeter and an ammeter is provided to measure the Input / Output voltage and current.
Front Panel Details:
1.
AC input
:
Terminals to connect AC input
2.
AC output
:
AC supply terminals after the MCB to be connected to
power circuit.
3.
MCB
:
A 6A / 2 pole MCB for ON/OFF the AC supply to the
power circuit
4.
T1 & T2
:
SCR’s 16 Amps / 600 volts
5.
D3 & D4
:
Diodes – 16amps / 600V
6.
Dm
:
Free wheeling diode
7.
TR
:
Triac – 10 amps / 600 volts
8.
Voltmeter
:
3 ½ Digit digital AC/DC Voltmeter to measure input /
output voltage
9.
Ammeter
:
3 ½ Digit digital AC/DC Ammeter to measure current
Procedure:
Make the inter connections in the power circuit as given is the circuit diagram. Switch ON the
firing circuit and observe the trigger outputs.
Make sure that the firing pulses are proper before
connecting to the power circuit.
Then connect the trigger output from firing circuit to corresponding SCR’s / Triac. In the power
circuit Initially set the AC input to 30 volts. Switch ON and MCB. Switch ON the Trigger outputs
switch. Select the SCR / Triac selection switch and observe the output wave forms across ‘R’ load by
varying the firing angle potentiometer. If the output wave form is proper then you can connect the motor
& increase the input voltage to rated value 0-230V gradually. Vary the firing angle and note down output
voltage and speed of the motor.
Note:
1) If you are not getting the output after all proper connections interchange AC output terminals, after
switch OFF the MCB. This is just to synchronize the power circuit with firing circuit.
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Result:
Thus the speed control of Universal motor is performed by varying armature voltage through phase
controlled converter
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Post lab questions
SPEED CONTROL OF UNIVERSAL MOTOR
1. What is Circuit Breaker & Fuse?
2. What are the different operating regions of SCR?
3. What is gate pulse?
4. What is snubber circuit?
5. Different methods of speed control?
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EXPT. NO.12:
Pre lab questions
VOLTAGE COMMUTATED CHOPPER
1. What are the other names of this circuit?
2. What are the commutating components of this circuit?
3. What are the different types of commutated choppers?
4. Give the expression for commutating elements L and C for the voltage commutated chopper.
5. What is the purpose of freewheeling diode?
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VOLTAGE COMMUTATED CHOPPER
Aim:
To observe the operation of class D commutated technique.
Apparatus Required:
1. Force commutation trainer kit.
2. Patch chord
3. CRO
CIRCUIT DIAGRAM
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Model Graph:
Tabular Column:
S.No.
Duty Cycle(%)
Output Voltage(V)
Time
period(ms)
1
2
3
Procedure:
1)
Patch the voltage commutated chopper as per the circuit diagram
2)
Connect the CRO probe across the commutated chopper
3)
Give the input dc voltage (0-30)v, 2amps from the external power supply.
4)
Switch ON the trainer then switch ON the input dc suuply circuit breaker.
5)
After then switch ON the trigger OFF-ON position
6)
From the capacitor output waveform we can measure the turn on time and turn off time of main
SCR as well as auxiliary SCR
7)
Verify the unity and frequency of the triggering circuit using parts provided on the triggering
circuit.
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8)
Also observe the voltage across main SCR and auxiliary SCR and load
9)
Take the turn on and turn off time at main so auxiliary SCR from the capacitor waveform at
various values of unity cycle and frequency and tabulate them
10)
Also find out the peak value of current through the capacitor
Theory:
MODE-1
Main SCR is triggered to make source current to flow in two path one is load current and other
path with triggering of SCR load get connected to supply and load voltage.
MODE-2
At a desired instant the auxiliary SCR is to be triggered for turning OFF the main SCR T1 with the
switch ON, T2 reverse capacitance voltage appears across T1 which reverse biases it and turn it OFF.
MODE-3
SCR T2 turn OFF since the capacitance is slightly changed after the freewheeling diode set
frequently forward biased.
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Result:
Thus the operation of class D commutated technique has been obtained.
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Post lab questions
VOLTAGE COMMUTATED CHOPPER
1. What are the initial conditions to be attained before the circuit can be operated?
2. What are the components required for commutating the thyristor?
3. What is the main disadvantage of this circuit?
4. In what mode does the diode and inductor operate?
5. Give the classification of the choppers.
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