A DC–DC CONVERTER WITH HIGH-VOLTAGE STEP-UP RATIO AND REDUCED- VOLTAGE STRESS FOR RENEWABLE ENERGY GENERATION SYSTEMS A Dissertation by Satya Veera Pavan Kumar Maddukuri Master of Science, University of Greenwich, UK, 2012 Bachelor of Technology, Jawaharlal Nehru Technology University Kakinada, India, 2010 Submitted to the Department of Electrical Engineering and Computer Science and the faculty of the Graduate School of Wichita State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy December 2018 1 © Copyright 2018 by Satya Veera Pavan Kumar Maddukuri All Rights Reserved 1 A DC–DC CONVERTER WITH HIGH-VOLTAGE STEP-UP RATIO AND REDUCED- VOLTAGE STRESS FOR RENEWABLE ENERGY GENERATION SYSTEMS The following faculty members have examined the final copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirement for the degree of Doctor of Philosophy with a major in Electrical Engineering and Computer Science. ___________________________________ Aravinthan Visvakumar, Committee Chair ___________________________________ M. Edwin Sawan, Committee Member ___________________________________ Ward T. Jewell, Committee Member ___________________________________ Chengzong Pang, Committee Member ___________________________________ Thomas K. Delillo, Committee Member Accepted for the College of Engineering ___________________________________ Steven Skinner, Interim Dean Accepted for the Graduate School ___________________________________ Dennis Livesay, Dean iii DEDICATION To my parents, my wife, my in-laws, my teachers, and my dear friends iv ACKNOWLEDGMENTS Firstly, I would like to express my sincere gratitude to my advisor Dr. Aravinthan Visvakumar for the continuous support of my PhD study and related research, for his thoughtful patience, motivation, and immense knowledge. His guidance helped me in all the time of research and writing of this dissertation. I could not have imagined having a better advisor and mentor for my PhD study. Thanks, are also due to Dr. M. Edwin Sawan, Dr. Ward T. Jewell, Dr. Chengzong Pang, Dr. Thomas K. Delillo for their insightful comments, encouragement, and for the hard question which incented me to widen my research from various perspectives. My sincere thanks also go to Dr. John Watkins, Dr. Parlekar Tamtam, Dr. Richard Seals, and Dr. Yuri B. Shtessel, for their moral support. Thanks to WSU graduate school and NSF I-corps for providing the funds to develop and test the prototype. I am also grateful to the following university staff: Nathan Smith and Tom McGuire for their unfailing support and assistance in developing and testing the prototype circuit. I thank my fellow power quality lab mates in for the stimulating discussions, for the sleepless nights we were working together before deadlines, and for all the fun we have had in the last three years. Also, I thank my friends in the PDS group whom I consider as my extended family. And finally, last but by no means least, I would like to thank my parents, my wife and brother-in- law for supporting me spiritually throughout my PhD education and my life in general. Thanks for all your encouragement! v ABSTRACT This research work presents a high gain direct current–direct current (DC–DC) converter which is derived from a traditional boost converter. Electrical power systems are changing from a centralized generation model to a hybrid model with distributed generation. Distributed renewable energy sources such as photovoltaic (PV) modules, wind and fuel cells are becoming possible alternatives. However, to connect these systems to the grid, reliable DC–DC boost converters with high voltage gain is becoming a requirement. Firstly, a new open-loop DC–DC boost converter with superior performance in terms of voltage step-up ratio and reduced voltage stress on the switches, compared to other existing high gain DC–DC boost converter counterparts is proposed. Along with analyzing the operation principle of the proposed converter, design procedure and component selection procedures are presented in this report. Experimental results along with simulation results are provided to validate the fundamentals of the open-loop proposed converter. This converter can easily achieve a gain of 20 while benefiting from the continuous input current. Secondly, to effectively maintain the voltage output at the required level, closed loop dc-dc converter with Proportional–Integral-Differential (PID) controller was proposed and simulated. Thirdly a multi-loop with Proportional–Integral (PI) was proposed and simulated. Later, a charge controller was designed and operated along with closed loop dc-dc converter to supply load with two different voltage requirements. Simulation results are presented and analyzed to validate the theoretical results of the closed loop converter. Based on the simulation results the proposed controller can maintain the output voltage at the required level with respect to the changes in load. vi TABLE OF CONTENTS Chapter Page 1. INTRODUCTION .............................................................................................................. 1 2. LITERATURE REVIEW ................................................................................................... 4 2.1 DC–DC Boost Converters....................................................................................... 4 2.2 Controller for DC–DC Boost Converter ................................................................. 8 3. MOTIVATION AND PROPOSED WORK ..................................................................... 12 4. METHODOLOGY ........................................................................................................... 17 4.1 Modeling of Proposed Converter .......................................................................... 17 4.2.1 Mode-I....................................................................................................... 19 4.2.2 Mode-II ..................................................................................................... 19 4.2 Modified Proposed Converter ............................................................................... 21 4.2.1 Mode-I....................................................................................................... 22 4.2.2 Mode-II ..................................................................................................... 23 4.3 Analysis of the Proposed Converter ..................................................................... 24 4.3.1 Steady-State Conditions of Converter ...................................................... 25 4.3.3 Topologies Comparison ............................................................................ 27 4.4 Single loop controller ............................................................................................ 30 4.5 Pulse Width Modulation Generator with Saturation limiter ................................. 33 4.6 Single loop DC–DC boost converter with change in reference voltage ............... 34 4.7 Multi-loop controller ............................................................................................. 35 4.8 Full bridge DC-AC Converter .............................................................................. 41 5. RESULTS ......................................................................................................................... 43 5.1 Component Selection ............................................................................................ 43 5.1.1 Inductor Selection ..................................................................................... 43 5.1.2 Capacitor Selection ................................................................................... 44 5.1.3 MOSFET Selection ................................................................................... 45 5.2 Simulation Validation ........................................................................................... 48 5.2.1 Open-loop Simulation Results .................................................................. 48 5.2.2 Single-loop Simulation Results................................................................. 50 5.2.3 Single-Loop with Charge Controller Simulation Results ......................... 54 5.2.4 Multi-loop Controller Simulation Results ................................................ 55 5.2.5 Multiloop Controlled DC-DC Converter Response with Respect to Change in Input .................................................................................... 57 5.2.6 Output Voltage from the DC-AC Converter ............................................. 58 5.3 Experimental Validation ....................................................................................... 59 vii TABLE OF CONTENTS (continued) Chapter Page 5.3.1 PCB Design ............................................................................................... 60 5.3.1 System Test Results .................................................................................. 64 6. CONCLUSION ................................................................................................................. 67 7. REFERENCES ................................................................................................................. 69 viii LIST OF FIGURES Figure Page 1. General applications of DC–DC boost converters. ............................................................. 1 2. Isolated DC–DC boost converter (a) with two controlled