University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 12-2018 Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters Chongwen Zhao University of Tennessee, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Recommended Citation Zhao, Chongwen, "Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters. " PhD diss., University of Tennessee, 2018. https://trace.tennessee.edu/utk_graddiss/5269 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Chongwen Zhao entitled "Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Electrical Engineering. Daniel Costinett, Major Professor We have read this dissertation and recommend its acceptance: Fred Wang, Leon M. Tolbert, D. Caleb Rucker Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters A Dissertation Presented for the Doctor of Philosophy Degree University of Tennessee, Knoxville Chongwen Zhao December 2018 To my parents To Junting Guo ii Acknowledgement I would like to acknowledge the support and guidance from faculty members and staff at the University of Tennessee. My advisor, Dr. Daniel Costinett, always shares his passion and enthusiasm with me, on the path of pursuing my Ph.D. degree. This motivates me to accomplish my degree and refine myself as a human being. Dr. Leon Tolbert is a great mentor and talking to him is always my honor and pleasure. Dr. Fred Wang is an example of excellence and asking questions in his class gives me plenty of intellectual joy. Dr. Chien-fei Chen, Dr. Nicole McFarlane, Dr. Caleb Rucker, Dr. Donatello Materassi, Dr. Benjamin Blalock and Mr. Robert Martin give me many good advices during my study, and I would like to express my appreciation to them. I build beautiful friendships with my colleagues who came to UTK the same year, though some of them are out of town and having their marvelous adventures. Special appreciations to Dr. Bo Liu, Dr. Wenyun Ju and Mr. Ren Ren for numerous days working and hanging out together. The senior colleagues in the lab own sympathy and are helpful, a great trait of the CURENT center. The young generations are vigorous and working hard, paving a bright future. So glad that I have a great time here. The Doctor of Philosophy stems from the golden Greek time, and an experience expanding the knowledge boundary links me to those BIG names. No matter the world is physical or spiritual, may the knowledge long live. iii Abstract Harmonic content is inherent in switched-mode power supplies. Since the undesired harmonics interfere with the operation of other sensitive electronics, the reduction of harmonic content is essential for power electronics design. Conventional approaches to attenuate the harmonic content include passive/active filter and wave-shaping in modulation. However, those approaches are not suitable for resonant converters due to bulky passive volumes and excessive switching losses. This dissertation focuses on eliminating the undesired harmonics from generation by intelligently manipulating the spectrum of switching waveforms, considering practical needs for functionality. To generate multiple ac outputs while eliminating the low-order harmonics from a single inverter, a multi-frequency programmed pulse width modulation is investigated. The proposed modulation schemes enable multi-frequency generation and independent output regulation. In this method, the fundamental and certain harmonics are independently controlled for each of the outputs, allowing individual power regulations. Also, undesired harmonics in between output frequencies are easily eliminated from generation, which prevents potential hazards caused by the harmonic content and bulky filters. Finally, the proposed modulation schemes are applicable to a variety of DC/AC topologies. Two applications of dc/ac resonant inverters, i.e. an electrosurgical generator and a dual-mode WPT transmitter, are demonstrated using the proposed MFPWM schemes. From the experimental results of two hardware prototypes, the MFPWM alleviates the challenges of designing a complicated passive filter for the low-order harmonics. In addition, the MFPWM facilitates combines functionalities using less hardware compared to the state-of-the-art. The prototypes demonstrate a comparable efficiency while achieving multiple ac outputs using a single inverter. iv To overcome the low-efficiency, low power-density problems in conventional wireless fast charging, a multi-level switched-capacitor ac/dc rectifier is investigated. This new WPT receiver takes advantage of a high power-density switched-capacitor circuit, the low harmonic content of the multilevel MFPWMs, and output regulation ability to improve the system efficiency. A detailed topology evaluation regarding the regulation scheme, system efficiency, current THD and volume estimation is demonstrated, and experimental results from a 20 W prototype prove that the multi-level switched-capacitor rectifier is an excellent candidate for high-efficiency, high power density design of wireless fast charging receiver. v Table of Contents 1. Introduction ................................................................................................................................1 1.1 Applications of Resonant Converters ............................................................................. 4 1.1.1 Electrosurgical Power Supply .................................................................................. 5 1.1.2 Wireless Power Transfer System ............................................................................. 7 1.2 Summary ....................................................................................................................... 10 2. Harmonic Content in Resonant Converter ............................................................................12 2.1 Contributing Factors of Harmonic Content .................................................................. 13 2.2 Modulation Schemes for SMPS .................................................................................... 15 2.1.1 Carrier-based Pulse Width Modulation ................................................................. 15 2.2.2 Space Vector Modulation ...................................................................................... 16 2.2.3 Programmed Pulse Width Modulation................................................................... 18 2.3 Modulation and Control of Resonant Converter ........................................................... 19 2.4 Dissertation Organization ............................................................................................. 20 3. Literature Review ....................................................................................................................23 3.1 Harmonic Content Reduction Approach ....................................................................... 23 3.1.1 Hardware-based Approaches ................................................................................. 24 3.1.2 Software-based Approach ...................................................................................... 25 3.2 Programmed PWM ....................................................................................................... 26 3.2.1 Programmed PWM Problem Formation ................................................................ 26 3.2.2 Solving Algorithm ................................................................................................. 28 3.3 Multi-frequency Generation Approaches ..................................................................... 31 3.3.1 Separate-Converter Configuration ......................................................................... 31 3.3.2 Single-Converter Configuration ............................................................................. 35 3.4 Challenge and Motivation ............................................................................................. 37 vi 4. Multi-Frequency Programmed Pulse Width Modulation ....................................................38 4.1 Benchmark Evaluation .................................................................................................. 39 4.1.1 Duty Cycle Modulation.......................................................................................... 40 4.1.2 Carrier-based PWM ............................................................................................... 42 4.1.3 SHE ........................................................................................................................ 44 4.1.4 Summary ...............................................................................................................