DESIGN OF ZERO CURRENT SWITCHING RESONANT

DESIGN OF ZERO CURRENT SWITCHING RESONANT SWITCH DC-DC CONVERTER USING AN SCR DISSERTATION Submitted in partial fulfilment of the requirements of Master of Engineering in Electrical Power Engineering Vijayakumar Kunanayagam Department of Electrical and Electronics Engineering School of Engineering Kathmandu University December 2005 DESIGN OF ZERO CURRENT SWITCHING RESONANT SWITCH DC-DC CONVERTER USING AN SCR DISSERTATION Submitted in partial fulfilment of the requirements of Master of Engineering in Electrical Power Engineering By: Vijayakumar Kunanayagam Under supervision of: Dr. Peter Freere Associate Professor Department of Electrical and Electronics Engineering School of Engineering Kathmandu University Department of Electrical and Electronics Engineering School of Engineering Kathmandu University December 2005 ACKNOWLEDGEMENT First, I would like to thank my parents, brothers and sisters for their all time support. I wish to convey the warmest thanks to my supervisor Associate Professor Peter Freere and to Mr. Krishna Gurung, Department of Electrical & Electronics Engineering, School of Engineering, Kathmandu University, Nepal for their sincere and earnest guidance extended to me in all aspects. I am also very thankful to Associate Professor Bhupendra Bimal Chhetri and Assistant Professor Gautam Bajracharja, Department of Electrical & Electronics Engineering, School of Engineering, Kathmandu University, Nepal for their valuable ideas in my thesis work. Further, I would like to express my gratitude to Norwegian University of Science & Technology (NTNU), Norway and Kathmandu University (KU), Nepal for giving me the opportunity to do the Master of Engineering in Electrical Power Engineering with full NORAD scholarship. Finally, I am very thankful to all of my friends especially Mr. Herbert Innah, Indonesia and Mr. Brighton Chishala Kombe, Zambia and all the members of the Kathmandu University Power and Energy Group (KUPEG) for providing me help and timely suggestions when in need. ABSTRACT In an electrical vehicle, the operating dc voltages of the appliances such as electrical bulbs differ from the voltage available in the dc supply. Therefore, a dc-dc converter which is able to supply required power with high efficiency and reliability is required to either step up or down the voltage according to the operating voltage required. A 100/12V, 300W dc-dc converter is designed. Generally, in a step down dc-dc converter, as the required output voltage is obtained by turning on and off the entire load current through the switches, there are high switching power losses, high switching stresses and electromagnetic interferences. These reduce the efficiency and reliability of a converter. Therefore in this designed dc-dc converter turning on and off of a switch is carried out when current is zero to reduce the abovementioned losses and stresses by using a LC resonance principle. A thyristor is used as a switch because it has high reliability, robustness and high power capability and it will automatically turn off when current through it becomes zero. In the research work on the ZCS resonant switch dc-dc converter, the limitations of the resonance were found. Then the various converter configurations were investigated to insert a step down transformer to make the converter efficient. Afterwards, the power output of the converter was achieved 168W, 12V dc by investigating the limitations of power. The efficiency of the converter is 56.3% at loading of 168W, 12V dc. Finally, a regulator circuit is designed. TABLE OF CONTENTS Glossary of Abbreviations List of Symbols List of Figures List of Tables Chapter 1: Introduction 1.1 Objectives 1.2 Organization of the thesis Chapter 2: Theory of the ZCS Resonant Switch DC-DC Converters 2.1 Series resonant circuit theory 2.2 Simulation of series resonant circuit 2.3 Control of resonance using a thyristor with an anti-parallel diode and no load 2.4 Simulation of control of resonance using a thyristor with and antiparallel diode 2.5 Theory of series resonant circuit with a parallel constant current load 2.6 Simulation of series resonant circuit with a parallel constant current load 2.6.1 Simulation when Io is equal to zero 2.6.2 Simulation when Io is greater than zero 2.6.2.1 Simulation when Io is less than 38A 2.6.2.2 Simulation when Io is equal to 38A 2.6.2.3 Simulation when Io is greater than 38A 2.7 The ZCS resonant switch dc-dc converter theory 2.7.1 Mode I (when 0 < t < T1 ) 2.7.2 Mode II (when T1 < t < T2 ) 2.7.3 Mode III (when T2 < t < T3 ) 2.7.4 Mode IV (when T3 < t < T4 ) 2.8 Simulation of ZCS resonant switch dc-dc converter Chapter 3: Limitations of Resonance 3.1 Resonant capacitor and load limit the resonance 3.2 Resonant inductor limits the resonance 01 02 04 07 08 11 11 13 13 14 16 19 20 24 24 25 26 27 28 29 29 31 32 32 33 36 36 38 3.3 An anti-parallel diode across the thyristor limits the resonance 3.4 The inductance inside the resonant capacitor limits the resonance 3.5 The long tail of the current through the thyristor limits the resonance 3.6 The magnetic material of inductor core limits the resonance Chapter 4: Insertion of a Step-down Transformer 4.1 Introduction of a transformer into the converter 4.1.1 High input to output voltage ratio 4.1.2 To protect the load during the sudden collapse of the resonance 4.1.3 To isolate the output from the input 4.2 The transformer between the supply and the thyristor 4.3 The transformer between the resonant inductor and the resonant capacitor 4.4 The transformer across the resonant capacitor 4.5 Introduction of a secondary capacitor 4.6 Introduction of a filter inductor Chapter 5: Limitations of Power Output 5.1 High power output 5.2 The inductor L limits the power 5.3 The resonant inductor limits the power 5.4 The introduction of a small capacitor limits the power 5.5 The resonant capacitor limits the power 5.6 Further improvements on the power 5.7 The insertion of a step down transformer Chapter 6: Final Circuit with a Regulator 6.1 Final configuration of the ZCS resonant switch dc-dc converter 6.2 Regulator circuit 6.3 The explanation of the complete circuit of the converter 6.4 Output and efficiency of the converter Chapter 7: Conclusion and Recommendation Appendix A: Resonant Frequency of Series LC-circuit A.1 Determination of resonant frequency of series LC-circuit A.2 Phase shift method 39 41 45 46 49 49 49 49 50 50 51 52 54 54 57 57 57 60 62 65 67 69 71 71 75 77 80 82 84 84 85 A.3 Impedance method Appendix B: Thyristor Gate Drive Circuit Design B.1 MCT2E optocoupler B.2 BC548 NPN transistor B.3 Thyristor gate drive circuit Bibliography 86 87 87 87 88 91