International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 1 - Mar 2014
A Bridgeless SEPIC Converter Fed DC Drive with
Unity Power Factor and Reduced Output Voltage
Ripple
Suganya M1, Pratheeba C2
1
PG Scholar , Department of EEE1, Nandha Engineering College1,Erode1,Tamilnadu1
Assistant Professor2, Department of EEE2, Nandha Engineering College2,Erode2,Tamilnadu2
Abstract− A bridgeless SEPIC converter fed DC drive with unity
power factor and reduced output voltage ripple is proposed. The
proposed bridgeless SEPIC converter can achieve low output
voltage ripples by provides the closed loop Proportional-Integral
controller technique. The closed loop PI control technique is
used to eliminate the output voltage ripples so that the voltage
stability is maintained as well as the power factor is also
improved. The input is controlled by PI controller. The
proportional controller checks the error between actual and
reference values. The integral controller compensates the error
with the repeated sequence. Additionally the Zero Voltage
Switching method is implemented, which will reduce the high
voltage stress during the switching period and it also reduces the
losses. The DC drive is used as a load. The chopper controlled
technique is applied to control the speed of the DC drive. In this
method the input current in a switching period is proportional
to the input voltage and near unity power is achieved.
Keywords−
Bridgeless
converter,
Proportional-Integral
controller (PI), Single ended primary inductor converter
(SEPIC), Power factor correction (PFC).
I.
INTRODUCTION
The preferable type of power factor correction (PFC)
circuit is active PFC so it makes the load as like resister,
leading to near-unity power factor and generating negligible
harmonics in the input line current. Active power factor
correction
circuits are commonly employed in ac–dc
converters and switched-mode power supplies, to the demand
on high efficiency and low harmonic pollution, t h e s e
kinds of converters include a full-bridge diode rectifier on an
input current path. For that, the conduction losses on the
full-bridge diode occur. To solve this problem, bridgeless
converters have been introduced recently. In that bridgeless
converters the full-bridge rectifier is reduce or eliminate, and
hence their conduction losses are also reduce.
The SEPIC is stands for Single Ended Primary Inductor
Converter. SEPIC is a type of DC-DC converter which is
used in many other applications like mobile phone battery
charger, electronic ballast, telecommunications and Direct
Current(DC) Power supplies etc, In this converter the electric
potential at its output to be greater than, less than, or equal to
that of the supply voltage. The output of the SEPIC is
controlled by varying duty cycle of the power switches like
Metal-Oxide-Semiconductor
Field-Effect
Transistor
(MOSFET), Insulated Gate Bipolar Transistor (IGBT), and
Gate Turn off (GTO) etc.
ISSN: 2231-5381
Fig. 1 Bridgeless SEPIC converter circuit
A SEPIC is similar to the conventional buck-boost
converter, it has one additional advantages of having noninverted output (the output has the same voltage polarity as
the input). The SEPIC is capable of operating in either step
up or step down mode and widely used in battery operated
equipments. The SEPIC is exchanges the energy between the
capacitors and inductors in order to convert from one voltage
to another. The series capacitor is used to couple energy from
input to output. When the switch is turned off the capacitor
voltage falls to 0V. SEPIC converter is operated in two
modes, Continuous Conduction Mode (CCM) and
Discontinuous Conduction Mode (DCM).
SEPIC is said to be in continuous- conduction mode if the
current through the inductor never falls to zero. The DCM
mode operation means the inductor current falls to zero. It is
often identified by its use of two magnetic windings. These
windings can be wound on a common core. The SEPIC have
been designed to increase the Power Factor Correction (PFC),
in order to achieve the high power factor. In Fig.1, a
bridgeless SEPIC converter is shown. In Fig.1 the full bridge
diode is removed so that the component count is reduced and
it shows high efficiency due to the absence of the full-bridge
diode. An additional winding of the input inductor, an
auxiliary small inductor, and a capacitor, are includes in an
auxiliary circuit; it is utilized to reduce the input current
ripple. The coupled inductors are often used to reduce the
current ripple.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 1 - Mar 2014
II.
DESCRIPTION OF PROPOSED TOPOLOGY
The closed loop PI controller technique is used thereby the
output voltage is maintained stable and also it reduces the
output ripples. Power factor is further improved by using this
closed loop technique. The ZVS technique is implemented in
order to reduce the high peak voltage ripples during switch
on period. Hence it minimizes the losses. The DC Drive is
used as a load. The chopper controlled technique is applied to
control the speed of the DC drive.
Ac
Rectifier
Supply
SEPIC
PWM
V&I
Measurement
DC
Drive
PI
Controller
Converter
Pulse
Generator
Firing
Angle
Fig. 2 Proposed block diagram
The Fig.2 shows that the proposed block diagram of the
Bridgeless SEPIC converter. The AC input is given to the
rectifier. This will converts the AC supply into DC. In AC
conversion side, two same value inductors connected in
parallel. It will smooth the supply voltage and in the DC
conversion side the diode will combine the voltage of two
half cycle of supply voltage. Then the output of the SEPIC
converter is given to the load through the capacitor.
By measuring the input voltage and the current, the power
factor correction are made. PI controller is used to form a
closed loop and to control the duty cycle of the switches in
order to maintain the input current in phase with input
voltage. The proposed SEPIC with PI will provide feedback
control to regulate the output voltage. PWM technique is
used for giving the gate signal to the SEPIC converter. Firing
angle is given to the pulse generator to control the speed of
the DC motor. The output of the pulse generator is given to
the converter. The converters used are controlled rectifiers or
choppers. Here the chopper controlled techniques are used to
control the speed of the DC Drive. The DC motor control
system is designed and performed using a chopper circuit.
Chopper is a static power electronic device that
converts fixed dc input voltage to a variable dc output
voltage. Chopper systems have smooth control capability and
ISSN: 2231-5381
are highly efficient and fast in response. A chopper can be
used to step down or step up the fixed dc input voltage like a
transformer. DC motors are well known for their excellent
control of speed for acceleration and deceleration. It has the
various advantages such as simplicity, ease of application,
reliability and favorable cost; DC drives have long been a
backbone of industrial applications.
III. ANALYSIS OF THE PROPOSED CONVERTER
Fig. 1 shows the circuit diagram of the bridgeless SEPIC
converter. The circuit consist of an auxiliary circuit, that
includes an additional winding Ns of the input inductor Lc,
an auxiliary inductor Ls, and a capacitor Ca . The leakage
inductance of the coupled inductor Lc is included in the
auxiliary inductor Ls. The coupled inductor Lc is modeled as
a magnetizing inductance Lm and an ideal transformer which
has a turn ratio of 1: n (n=Ns /Np ). The capacitance of Ca is
large enough, So Ca can be considered as a voltage source
VCa during a switching period. Since the average inductor
voltage should be zero at a steady state, the average capacitor
voltage VCa is equal to the input voltage Vin during a
switching period. Similarly, the average capacitor voltage
VC1 is equal to Vin. Diodes D1 and D2 are the input rectifiers.
DS1 andDS2 are the intrinsic body diodes of the switches S1
and S2. Do is the output diode and Co is the output capacitor.
It is assumed that the converter operates in discontinuous
conduction mode, so the output diode Do is turned OFF
before the main switch is turned ON. The capacitance of the
output capacitor Co is assumed sufficiently large enough to
consider the output voltage Vo as constant. Also, the input
voltage is assumed constant and equal to Vin in a switching
period Ts. The magnetizing current Im varies from its
maximum value Im1 to its minimum value Im2. The inductor
current is varies from its maximum value Is1 to its minimum
value –Is2.
A. Mode 1 [t0,t1 ]
The operation of the SEPIC converter in one
switching period Ts can be divided into three modes.
Fig. 3 Mode 1 operation
Before t0, the switch S1 and the diode Do are turned OFF
and the switch S2 is conducting. In this mode of operation the
switch S1 and the switch S2 is conducting. The circuit diagram
of this mode 1 operation is shown in the Fig.3 At t0, the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 1 - Mar 2014
switch S1 is turned ON and the switch S2 is still conducting.
Since the voltage Vp across Lm is Vin, the magnetizing current
im is increases from ita minimum value.
B. Mode 2 [t1,t2]
In the mode 2 operation the switch S1 is turned OFF and
the output diode D0 is conducting. The circuit diagram of mode
2 operation is shown in the Fig.4.
Fig. 4 Mode 2 operation
At t1, the switch S1 is turned OFF and the switch S2 is still
conducting. Since the voltage Vp across Lm is −Vo, the
magnetizing current im is decreases from its maximum value.
C. Mode 3 [t2,t0’]
In the mode 3 operations the switch S2 is conducting and
the switch S1 is in turned OFF condition.
Fig. 5 Mode 3 operation
The circuit diagram of mode 3 operation is shown in the
Fig.5. The output diode is turned OFF during this mode of
operation. At t2 , the current iDo becomes zero, and the diode
Do is turned OFF.
IV. POWER FACTOR CORRECTION
The most loads in modern electrical distribution systems
are inductive there is an ongoing interest in improving power
factor. The low power factor of inductive loads can adversely
affect voltage level. As such, power factor correction through
the application of capacitors is widely practiced at all system
voltages. As utilities increase penalties they charge customers
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for low power factor, system performance will not be the
only consideration. The installation of power factor
correction capacitors improves system performance and saves
money. Although the methodology for applying capacitors is
relatively straight forward, there are a number of influencing
factors that must be considered.
A. Power Factor
Power factor (PF) is the name given to the ratio of the
active or usable power measured in kilowatts (KW), to the
total power (active and reactive) measured in kilovolt
amperes (KVA). Power Factor = KW / KVA. The total power
supplied to inductive equipment is the vector sum of KW and
KVA. The Displacement Power Factor is the cosine of the
angle between these two quantities. The value for the power
factor can theoretically where a value of 100% also called
unity power factor delivers all of the power as active power.
A value of 0% would mean all the power is supplied as
reactive power; no motors would turn and no useful work
could be accomplished. Electric utility companies must
supply the entire KVA demand. Since a customer only
achieves useful work from the KW portion, a high power
factor is important.
B. Power Factor Improvement
In order to understand power factor, one must first
know the process of energy storage in capacitors and
inductive devices. As the voltage in A.C. circuits varies
sinusoidal, it alternately passes through zero and starts toward
maximum voltage. During this time, the inductive device
gives up energy from its electromagnetic field, and the
capacitor stores energy in its electrostatic field. As the
voltage passes through a maximum point and starts to
decrease, the capacitor gives up energy and the inductive
device stores energy. Thus, when a capacitor and an inductive
device are installed on the same circuit, there will be an
exchange of magnetizing current between them, that is, the
leading current taken by the capacitor neutralizes the
magnetizing current to the inductive device. The capacitor
may be considered to be a Kilo Volt Amp-Reactive (KVAR)
generator, since it actually supplies magnetizing requirements
in the inductive device.
C. Power Factor Correction
The power factor correction method is improves the
efficiency of the converter. Power factor correction is the
method of correcting the power factor closer to one. Power
factor correction is applied to different applications such as
in: electrical power transmission utilities to improve the
stability and efficiency of the transmission network. There
are several advantages in utilizing power factor correction
capacitors that is increased load carrying capabilities in the
circuits, improved voltage and reduced power system losses.
AC power flow has the three components: real power (also
known as active power) (P), measured in watts (W); apparent
power (S), measured in volt-amperes (VA); and reactive
power (Q), measured in reactive volt-amperes (VAR). In the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 1 - Mar 2014
case of a perfectly sinusoidal waveform, P, Q and S can be
expressed as vectors that form a vector triangle such that,
Q +P = S
(1)
If ϕ is the phase angle between the current and voltage,
then the power factor is equal to the cosine of the angle, cos
∅, and
⎤P⎜=⎜S⎤ ⎤ COS ∅⎤
(2)
Since the units are consistent, the power factor is by
definition a dimensionless number between 0 and 1. When
power factor is equal to 0, the energy flow is entirely
reactive, and stored energy in the load returns to the source
on each cycle. When the power factor is 1, all the energy
supplied by the source is consumed by the load. Power
factors are usually stated as "leading" or "lagging" to show
the sign of the phase angle. If a purely resistive load is
connected to a power supply, current and voltage will change
polarity in step, the power factor will be unity (1), and the
electrical energy flows in a single direction across the
network in each cycle. Inductive loads such as transformers
and motors (any type of wound coil) consume reactive power
with current waveform lagging the voltage. Capacitive loads
such as capacitor banks or buried cable generate reactive
power with current phase leading the voltage.
V. PI CONTROLLER
In the automatic control systems the reference input will
be an input signal; it is proportional to desired output. The
error detector compares the reference input and feedback
signal and if there is a difference it produces an error signal.
The controller modifies the error signal for better control
action. The controllers are used in the system to produce a
control signal necessary to reduce the error signal to zero or
to small value. In most of the system the controller itself
amplifies the error signal and integrates or differentiates to
produce a control signal. This is a control mode that results
from a combination of proportional mode and the integral
mode. The analytic expression for this control process is
found from a series combination of proportional and integral
controller.
PI controller makes a closed loop to control the power
factor during load regulation. PI is a control feedback
mechanism widely used in industrial applications. It corrects
the error between a measured variable. General approach to
tuning is initially have no integral gain, Increase Kp until get
satisfactory response, Start to add in integral until the steady
state error is removed in satisfactory time (may need to
reduce KP if the combination becomes oscillatory).
VI.
SIMULATION RESULTS
The proposed converter is simulated by MATLAB
(R2011a) and the simulated waveforms are shown in fig. The
SEPIC is exchanges energy between the capacitors and
inductors in order to convert from one voltage to another. To
couple energy from input to output the series capacitor is
used. The proportional controller checks the error between
actual and reference voltage. The integral controller will
ISSN: 2231-5381
compensate the error by comparing error with repeated
sequence. The value again compared with PWM signal.
Output from PI controller is compared with repeated
sequence. The bridgeless SEPIC converter simulation
diagram is shown in Fig.5.
Fig. 6 Simulation diagram of the SEPIC converter
The chopper controlled technique is applied to control the
speed of the DC motor. During the period Ton, chopper is on
and load voltage is equal to source voltage Vs. During the
period Toff, chopper is off, load voltage is zero. In this
manner, a chopped dc voltage is produced at the load
terminals. When the switch is off, no current can flow and
when switch is on, the current flows through the load. In the
proposed system the efficiency is achieved 98% and the
ripples are reduced by using the closed loop PI control
method. The power factor is achieved nearly unity. The table
1 shows the simulation parameters of the DC machine.
TABLE I
SIMULATION PARAMETERS OF A DC MACHINE
Parameters
Armature resistance(Ra)
Values
2.581Ω
Armature inductance (La)
0.028H
Field resistance(Rf)
281.3Ω
Field inductance(Lf)
156H
Rated field voltage(Vf)
300 volts
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 1 - Mar 2014
The Fig.7 shows the input voltage. It is given to the SEPIC
converter. In that the input is AC. By using the diode rectifier
in the input side of the SEPIC converter convert it into DC. In
Fig.8 shows the input current waveform.
In the Fig.10 shows that, the speed of the DC Drive. The
chopper control technique is used to control the speed of the
DC motor.
Fig. 10 Speed response of the motor
The active power and reactive power of the system is
shown in Fig.11. The power factor waveform is shown in the
Fig.12. In that the line current is in phase with line voltage it
will improve the Power factor of this circuit. This improved
power factor will increase system reliability.
Fig. 7 Input voltage waveform
Fig. 8 Input current waveform
The Fig.9 shows that the output voltage of the SEPIC
converter. The PI will provide optimum convergence to the
output value.
Fig. 9 Output voltage waveform
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Fig. 11 Active and reactive power waveform
Fig. 12 Power factor correction
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International Journal of Engineering Trends and Technology (IJETT) – Volume 9 Number 1 - Mar 2014
VII. CONCLUSION
A bridgeless SEPIC converter fed DC drive with unity
power factor and reduced output voltage ripple is proposed.
As a result, it can be seen that the SEPIC converter
substantially increased the power factor and reduces the
output voltage ripples. In order to eliminate the input bridge
diodes, efficiency is improved. In addition, the input current
ripple is reduced by utilizing an additional winding of the
input inductor and an auxiliary capacitor. The closed loop PI
control technique is used to eliminate the output voltage
ripples so that the voltage stability is maintained as well as
the power factor also improved. The proportional controller
checks the error between actual and reference values. The
integral controller will compensate this error by comparing
error with repeated sequence. The value again compared with
PWM signal. The usage of PI controller will reduce the error
between reference and actual value. Additionally the ZVS
method is implemented, which will reduces the high voltage
stress during the switching period and it also reduces the
losses. The chopper controlled technique is applied to control
the speed of the DC drive.
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ISSN: 2231-5381
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M.Suganya was born in Erode,
Tamilnadu on 03rd April 1989 and
received her BE Degree in
Electrical
&
Electronics
Engineering from Vivekanandha
college of engineering for women
Tiruchengode, in April 2010.
Currently she is pursuing her ME
Degree in Power Electronics &
Drives from Nandha Engineering
College, Erode. Her research
interest includes power electronics
C.Pratheeba was born in Erode,
Tamilnadu on 27th June 1986. She
received her BE Degree at Vellalar
college of Engineering and
Technology in April 2008 and
received her M.E degree in part
time at Muthayammal Engineering
College in July, 2012. She is
having a total of 4 years and 6
months teaching experience. She is
presently working as Assistant
Professor in the department of
Electrical
and
Electronics
Engineering
in
Nandha
Engineering college Erode.
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