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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 , . 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 . 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) . The passive filters exhibit high efficiency but they are bulky and heavy . 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) . 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  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 , . 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  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 . 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 - such as natural near-unity power factor , 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 -. 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.   Table 2. Comparison of controllers for type-3 bridgeless Cuk PFC circuit. Controllers Power Factor PI Fuzzy Logic Controller  0.9710 0.9844 6. Conclusions  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.    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 References  Abbas A. Fardoun, “New efficient bridgeless Cuk rectifiers for PFC applications,” IEEE Trans. on       Power Electronics, vol. 27, no.7, pp. 3292-3300, 2012. Ahmad J. Sabzali, “New bridgeless DCM sepic and Cuk PFC rectifiers with low conduction and switching losses”, IEEE Trans. on Industrial Applications, vol. 47, no. 2, pp. 873-881, 2011. J. P. Mishra and R. Rath, “Input power factor correction using buck converter in single phase AC-DC circuit,” Thesis, National Institute of Technology, Rourkela, 2010. D. Tollik and A. 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Balamurugan et al.: Power Factor Improvement using Single Phase Bridgeless Cuk Converter Topology       Cuk PFC converter,” International Journal of Innovative Technology and Exploring Engineering (IJITEE), vol. 1, no. 2, pp. 204-210, 2012. Q. Yu, “Fuzzy logic and digital PI control of single phase power factor preregulator for an online UPS-a comparative study,” In Proc. of IEEE International Conference on Industrial Technology, pp. 103-107, Shanghai, 1996. Y.-S. Roh, “Active power factor correction (PFC) circuit with resistor-free zero-current detection,” IEEE Trans. on Power Electronics, vol. 26, no. 2, pp. 630-637, 2011. M. Gopinath and S. Ramareddy, “Simulation of closed loop controlled Bridgeless PFC boost converter,” Journal of Theoretical and Applied Information Technology, vol. 10, no. 1, pp. 103-108, 2009. R. Periyasamy, “Power factor correction on fuzzy logic controller with average current mode for DC-DC boost converter,” International Journal of Engineering, Research and Applications, vol. 2, no. 5, pp. 771-777, 2012. K. D. Purton and R. P. Lisner, “Average current mode control in power electronic converters– analog versus digital,” IEEE Trans. on Power Electronics, vol. 8, no. 2, pp. 102-523, 2006. Y. Zhang, W. Xu, and Y. Yu, “The PFC with Average Current-Mode and Voltage Fuzzy Controller for the Output Voltage,” In Proc. Second International Symposium on Intelligent Information Technology Application, vol. 1, pp. 771-775, Shanghai, 2008. 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.