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Transcript
480
International Journal of Fuzzy Systems, Vol. 15, No. 4, December 2013
Power Factor Improvement Using Single Phase Bridgeless Cuk Converter
Topology Based on Fuzzy Logic Control
R. Balamurugan, R. Nithya, and R. Senthilkumar
Abstract1
This paper deals with a new Cuk Topology for
Power Factor Correction (PFC). Most of the
front-end PFC converters are implemented using diode bridge and this results in the lower efficiency due
to significant losses with reduced power factor. This
new Cuk converter is a bridgeless Cuk PFC converter with two semiconductors switches. The current
flow path in converter during each interval of the
switching cycle reduces the conduction losses compared to the conventional Cuk PFC Rectifier. The
converter also offers natural protection against inrush current occurring at start-up, lower input current ripple, and less Electromagnetic Interference
(EMI). It has both continuous input and output currents with a reduced current ripple. Hence it is mostly preferred compared to the other PFC topologies
like boost, and buck-boost. It uses the simple control
strategy for controlling the power factor and offers
zero current turn ON and turn OFF for power
switches. It is also made to work in the Discontinuous
Conduction Mode (DCM) to achieve almost a unity
power factor and low distortions in the input current.
To observe the performance of this converter, a model based on the Cuk topology has been designed and
developed by using MATLAB/ SIMULINK software
and implemented with Proportional-Integral (PI) and
Fuzzy logic controller. The simulations are demonstrated in order to validate the effectiveness of the
controllers in power factor improvement.
Keywords: Cuk Bridgeless Topology, Fuzzy Logic Controller (FLC), Power Factor Correction (PFC), Proportional-Integral (PI) Controller.
1. Introduction
Corresponding Author: R. Balamurugan is with the Department of
Electrical and Electronics Engineering, K. S. Rangasamy College of
Technology, Tiruchengode.
E-mail: [email protected]
R. Nithya is with the Department of Electrical and Electronics Engineering, K. S. Rangasamy College of Technology, Tiruchengode.
Email: [email protected]
R. Senthilkumar is with the Department of Electrical and Electronics
Engineering, Erode Sengunthar Engineering College, Thudupathi.
Manuscript received 29 Aug. 2013; revised 1 Dec. 2013; accepted 20
Dec. 2013.
Recently power factor correction circuits have become
attractive for low and medium power applications since
several regulations have been put forth for regulating the
mains current. High power quality improvement is
needed for the power supply system in order to comply
with the international power quality standards. So for
this purpose, the switched mode DC-DC converters are
commonly used as the power factor correction circuits in
recent years especially for low power applications [1],
[2]. These circuits ensure high power factor at the input
side and emulate a purely resistive operation.
Present day single stage power factor correction circuits suffer from any one of these following issues:
1. High component voltage and current stresses
2. Low frequency oscillations in the output
3. Higher ripple content in the output voltage
4. Higher circuit complexity
5. Large number of components usage
Traditionally, diode bridge front end rectifiers of the
electronic equipment draw pulsed current from the utility
and affect the line voltage. This also introduces the electromagnetic interference and it leads to poor utilization
of the utility [3]. In compliance with the harmonic regulations, many power factor corrected AC-DC converters
have been proposed. The approaches like passive and
active power factor correction are used to improve the
power factor with reduced line current Total Harmonic
Distortion (THD) [4]. The passive filters exhibit high
efficiency but they are bulky and heavy [5]. Several active PFC have been introduced in the literature, like
boost, buck-boost, Cuk, single ended primary inductance
converter (SEPIC), but have their own drawbacks.
The features of the good power factor correction circuit are as follows:
1. A well regulated output voltage
2. Isolation between input AC mains and output DC
mains
3. A sinusoidal line current with minimum THD that
meets the requirements of international standards
4. High efficiency by eliminating or reducing the conduction and switching losses
5. Small size of the components used with reasonable
current and voltage ratings
So as to incorporate the above features, the converters
should be operated in Continuous Conduction Mode
© 2013 TFSA
R. Balamurugan et al.: Power Factor Improvement using Single Phase Bridgeless Cuk Converter Topology
481
To overcome these drawbacks, several bridgeless to(CCM) and Discontinuous Conduction Mode (DCM) [6].
On the other hand, the mostly used basic PFC comprises pologies, which are suitable for step-up/step-down apa front end rectifier which is followed by DC-DC con- plications have been recently introduced. It also suffers
from having three semiconductors in the current conducverter.
tion path during each switching cycle. A bridgeless PFC
rectifier based on the Single Ended Primary-Inductance
Converter (SEPIC) topology [9] have been also introduced but it has its own disadvantage of discontinuous
output current resulting in a relatively high output ripple.
The next topology used for the low input applications
is the Cuk converter. It offers several advantages in PFC
applications, such as isolating the transformer of a circuit
in easy way, natural protection against inrush current
occurring at start-up or overload current, lower input
current ripple, and less electromagnetic interference
(EMI) associated with the Discontinuous Conduction
Figure 1. Classical Cuk PFC converter.
Mode (DCM) topology. Unlike the SEPIC converter, the
In this conventional PFC rectifier (Fig.1), during the Cuk converter has both continuous input and output curswitch ON-time, the current flows through two rectifier rents with a low current ripple [10], [11]. Thus, for apbridge diodes and the power switch (Q) and during the plications, which require a low current ripple at the input
switch OFF-time current flows through two diodes of and output ports of the converter, the Cuk converter
Rectifier Bridge and the output diode (Do). Thus, three seems to be a potential candidate in the basic converter
semiconductor devices are involved during each switch- topologies.
There are three bridgeless Cuk converter topologies.
ing cycle. As a result, voltage drop across the bridge diThey
are Type1, Type2 and Type3 PFC rectifiers. Out of
ode causes a significant conduction loss, and heat generthose
three Cuk PFC rectifiers, Type 2 has the lowest
ated due to that may damage the diodes. These losses
would degrade the converter’s efficiency especially at a number of semiconductors but it has two drawbacks. It
low line input voltage. So, it becomes necessary to de- has floating switch and requires complex driver circuitry
sign a high current handling bridge rectifier with good for operating it. Thus, it causes higher electro-magnetic
heat dissipating characteristics. It should be less cost emissions. Type 1 also has the advantage of a lower
with less number of components. Research has been fo- component count, but a higher current peak. Type 3 has a
cused on this reason, recently inorder to have bridgeless higher component count, but lower stresses and higher
topologies [7] for improving the efficiency of the con- efficiency compared with the other Cuk derived bridgeverter. In this paper, a bridgeless topology is taken and less PFC rectifiers. So, Type-3 PFC rectifier circuit is
considered for this power factor correction.
its performance is analyzed.
2. Bridgeless PFC Topologies
3. Modes of Operation for Type-3 Cuk PFC
Rectifier
In order to maximize the power supply efficiency, researches have been directed toward the development of
efficient bridgeless PFC circuit topologies. Compared to
the conventional PFC circuit, bridgeless PFC circuit allows the current to flow through a minimum number of
switching devices. The converter conduction losses can
significantly be reduced and thus resulting in high efficiency with cost savings [8]. The basic and highly used
bridgeless topologies are boost-type circuit configuration
because of the low cost and high efficiency. The major
drawbacks are, higher dc output voltage than the peak
input voltage, difficulties in implementation of isolation
between input and output, high inrush current at startup,
and problem arising due to the current limitation during
overload conditions.
The analysis assumes that the converter is operating at
a steady state in addition to the following assumptions:
pure sinusoidal input voltage, ideal lossless components,
and all capacitors are large enough such that their
switching voltage ripples are negligible during the
switching period Ts. From Fig. 2, during the positive
half-line cycle, the first DC–DC Cuk circuit,
L1–Q1–C1–Lo1–Do1, is connected to the input AC source
through diode Dp and thus, it reaches the output. During
the negative half-line cycle, as shown in Fig. 3, the second DC–DC Cuk circuit, L2–Q2–C2–Lo2–Do2, is active
through diode Dn, which connects the input AC source to
the output. The circuit is analyzed during positive half
cycle of the input voltage.
482
International Journal of Fuzzy Systems, Vol. 15, No. 4, December 2013
shown in Fig.6.
Figure 2. Operation of type-3 converter during positive half
cycle.
Figure 4. Stage 1 operation of type-3 converter.
Accordingly, the peak current through the active
switch Q1 is given by
V
(1)
I Q1,peak  m D1Ts
Le
where Vm is the input voltage peak amplitude, D1 is the
duty cycle for switch, and Le is the parallel combination
of inductors L1 and Lo1.
Figure 3. Operation of type-3 converter during negative half
cycle.
The operation of the proposed rectifier is illustrated
assuming that the three inductors are operating in DCM.
The operation of the rectifier in DCM offers several advantages [12]-[14] such as natural near-unity power factor [8], turn ON of power switches at zero current, and
the output diodes (Do1 and Do2) are turn OFF at zero
current. This reduces the conduction loss of the diodes.
The circuit operation in DCM can be divided into
three distinct operating stages during one switching period Ts.
A. Stage 1 operation [t0, t1]
This stage starts when the switch Q1 is turned ON as
shown in Fig. 4. Diode Dp is forward biased by the inductor current iL1. As a result, the diode Dn is reverse
biased by the input voltage. The output diode Do1 is reverse biased by the reverse voltage (vac + Vo), while Do2
is reverse biased by the output voltage Vo.
In this stage, the currents through inductors L1 and Lo1
increase linearly with the input voltage, while the current
through Lo2 is zero due to the constant voltage across C2.
The inductor current of L1 and Lo1 during this stage is
B. Stage 2 operation [t1, t2]
This stage starts when the switch Q1 is turned OFF
and the diode Do1 is turned ON simultaneously providing
a path for the inductor currents iL1 and iLo1. Fig. 5 shows
the stage 2 operation of the circuit. The diode Dp remains
conducting to provide a path for iL1.
Figure 5. Stage 2 operation of type-3 Cuk converter.
Diode Do2 remains reverse biased during this interval.
This interval ends when iDo1 reaches zero and Do1 be-
R. Balamurugan et al.: Power Factor Improvement using Single Phase Bridgeless Cuk Converter Topology
483
comes reverse biased. It should be noted that the diode
Do1 is switched OFF at zero current.
The capacitor C1 is being charged by the inductor current
iL1. This period ends when Q1 is turned ON.
C. Stage 3 operation [t2, t3]
During this interval, only the diode Dp conducts to
provide a path for iL1 as shown in Fig. 7. Accordingly, the
inductors in this interval behave as constant current
sources.
4. Simulation Study
The MATLAB/SIMULINK model for bridgeless Cuk
converter for power factor correction is shown in Fig 8.
The circuit is controlled by using PI and Fuzzy logic
controllers. The circuits are operated in DCM mode and
it uses voltage follower control technique for reducing
harmonics.
A. PI controller for Cuk converter
Fig. 8 gives the control of input current harmonics by
using PI controller. The actual output voltage and reference voltage are compared and error is given as the input
to the PI controller [15-17]. The gain values of PI controller are adjusted in such a way in order to give pure
input supply current at unity power factor by controlling
the switching of converter. The gain values for obtaining
the power factor improvement here is kp=0.1 and ki=0.1
respectively.
Figure 6. Switching waveform of switches in Cuk PFC converter.
Figure 7. Stage 3 operation of type-3 Cuk PFC converter.
Hence, the voltage across the three inductors is zero.
Figure 8. PI controlled bridgeless type-3 Cuk PFC converter.
B. Fuzzy logic controller for Cuk converter
Fig. 9 shows fuzzy controlled bridgeless Cuk PFC
converter. The Mamdani fuzzy inference system is used
to control the converter circuit [18]-[20]. The fuzzy inference system uses the following.
 Triangular membership functions
 Fuzzification is done by using continuous universe of
discourse
 Implication using the “min” operator
 Defuzzification using the “centroid” method.
The fuzzy controller works with the triangular membership function variables. The inputs of the fuzzy logic
controller are error and change in error voltage. Fig.10
shows the input and output membership function assigned for the power factor correction.
484
International Journal of Fuzzy Systems, Vol. 15, No. 4, December 2013
Figure 9. Fuzzy logic controlled bridgeless type-3 Cuk PFC
converter.
Table 1 contains five linguistic variables for error
voltage and five linguistic variables for changing error
voltage. They are Negative Big (NB), Negative Small
(NS), Zero (Z), Positive Big (PB), and Positive Small
(PS). The 25 fuzzy rules are made using two input variable membership function. These rules are framed for
improving the power factor correction and are given as
follows:
If (e is Ai) and (ce is Bi) then (u is Yi)
where, e is error voltage, ce is change in error voltage
and u is the output from the fuzzy controller which is
given for switching the Cuk converter switches. Ai, Bi is
the input membership functions and Yi output membership function. Using the min operator as an inference
method and fuzzy centroid defuzzification formula for
weighting all the rule contributions, the crisp value of
the control variable is obtained and the corresponding
switches in the Cuk converter are operated. This gives
the input power factor correction.
5. Results and Discussion
A. PI based Cuk converter
The input voltage waveform observed from the simulink model of PI Controlled Bridgeless Type-3 Cuk PFC
Converter is shown in Fig. 11 and it contains fewer harmonics. 100 Vrms (141V peak to peak) voltages are applied as the input to the simulation. Thus, the Cuk converter work in DCM mode and gives buck operation.
Figure 11. Input voltage waveform of PI controlled Cuk PFC
converter.
Figure 10. Input and output membership variables.
Table 1. Fuzzy rule table.
e
ce
NB
NS
Z
PS
NB
NB
NB
NB
NS
PB
Z
NS
NB
NS
NS
Z
PS
PB
Z
NB
NS
Z
PS
PS
NS
Z
PS
PS
PB
PB
Z
PS
PB
PB
PB
Figure 12. Input current waveform of PI controlled Cuk PFC
converter.
Fig. 12 shows the input current and it contains some
harmonics. The input current obtained is nearly sinusoi-
R. Balamurugan et al.: Power Factor Improvement using Single Phase Bridgeless Cuk Converter Topology
485
dal and in phase with supply voltage. Thus PI controller
Input voltage is 100Vrms (141V peak to peak) and
improves the power factor compared to conventional output voltage observed is 50V in buck operation. The
Cuk PFC circuit. The output current obtained is 3.3 harmonics in the input voltage are reduced compared to
Amps and the waveform observed after the tuning of PI PI controlled Cuk PFC circuit.
controller is given in Fig. 13. The output voltage obtained is 50V for 100 RMS input and this is shown in Fig.
14.
Figure 17. Output voltage waveform of fuzzy tuned Cuk PFC
converter.
Figure 13. Output current waveform of PI controlled Cuk PFC
converter.
Figure 18. Output current waveform of fuzzy tuned Cuk PFC
converter.
Figure 14. Output voltage waveform of PI controlled Cuk
PFC converter.
B. Fuzzy controlled Cuk converter
The input voltage and current waveforms taken from
the simulation of fuzzy logic controller with the type- 3
Cuk rectifier are shown in Fig. 15 and Fig. 16.
The framed fuzzy rules work on this circuit and reduce the supply current harmonics. This is achieved by
the proper switching of the switches in the converter.
The output voltage and current waveforms observed after simulating the bridgeless Cuk converter with fuzzy
logic controller are shown in Fig. 17 and Fig. 18. Input
current waveform is distortion less compared to PI controller and is sinusoidal with input voltage.
Figure 15. Input voltage waveform of fuzzy tuned Cuk PFC
converter.
Figure 16. Input current waveform of fuzzy tuned Cuk PFC
converter.
Figure 19. Power factor for various input voltages of bridgeless Cuk PFC converter.
486
International Journal of Fuzzy Systems, Vol. 15, No. 4, December 2013
Fig. 19 shows the comparison chart of power factor
for various input voltages by use of PI and Fuzzy logic
controller. The power factor obtained after the simulation
of the both controllers is tabulated in Table 2. The fuzzy
logic controller gives the good power factor correction
compared to the PI controller.
[2]
[3]
Table 2. Comparison of controllers for type-3 bridgeless Cuk
PFC circuit.
Controllers
Power Factor
PI
Fuzzy Logic Controller
[4]
0.9710
0.9844
6. Conclusions
[5]
In this paper, the Bridgeless Cuk Topology for power
factor correction has been simulated with PI and Fuzzy
controller and results were presented. This converter topology uses reduced number of power switches compared to conventional Cuk PFC converter and operates
under DCM operation to produce less current ripple,
thereby improving the power factor. When comparing
the PI controller with fuzzy controller, Fuzzy controller
improves power factor nearer to unity. The measured
power factor using fuzzy controller shows 1% improvement in comparison to the PI controller. The MATLAB/SIMULINK software model has been used to validate the proposed work for power factor improvement.
[6]
[7]
[8]
Appendix
Parameters
Range
Line voltage
100 Vrms
Frequency
50 Hz
Output voltage
48 volt
Active switch(es) Q1and Q2
Snubber resistence 10k Ω
Input inductors L1 and L2
1mH
Output inductors Lo1and Lo2
22mH
Input capacitors C1 and C2
1 μF
Filter capacitor Co
12000μF
Input diodes Dp and Dn
200V,2A,Vf =0.7V
Output diodes Do1 and Do2
300V,10A,Vf=0.9V
Kp and Ki
0.1and 0.1
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R. Balamurugan received his B.E degree in Electrical and Electronics Engineering from Anna University Chennai,
in 2005 and he completed his post graduate studies in Power Electronics and
Drives from Anna University Chennai in
2007. He completed his PhD in the area
of power electronics from Anna University Chennai, in 2012. Presently, he is
working as Associate professor in the Department of Electrical
and Electronics Engineering, K.S.Rangasamy College of
Technology, Tiruchengode. He has published 22 papers in the
International Journals/ Conferences. He is a life member of
Indian Society for Technical Education (ISTE), New Delhi.
His current interests include Power Electronics, Power Quality,
Intelligent Control and PFC Converters.
487
R. Nithya received her B.E degree in
Electrical and Electronics Engineering
from Anna University Chennai in 2009
and she completed her post graduate
studies in Power Electronics and Drives
from Anna University Chennai in 2013.
She is presently working as Assistant
professor in the Department Electrical
and Electronics Engineering, K. S. Rangasamy College of Technology, Tiruchengode. Her research
interests include Power Converters, Power Factor Correction
and Intelligent Control.
R. Senthilkumar received his B.E degree in Electrical and Electronics Engineering from Anna University Coimbatore in 2011. He completed his post
graduate in Power Electronics and
Drives from Anna University Chennai in
2013. He is now working as Assistant
professor in the Department of Electrical
and Electronics Engineering, Erode
Sengunthar Engineering College, Thudupathi. His recent research interests include PFC Converters, DC-DC Converters
and Fuzzy Logic Control.