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Tian JL, Hu P. 2017. Adjusting the frequency of an autonomous push–pull converter for wireless power transfer through a voltage-controlled variable capacitor structure. Wireless Power Transfer 4(1): 69-75 doi: 10.1017/wpt.2017.3 
Adjusting the frequency of an autonomous push–pull converter for wireless power transfer through a voltage-controlled variable capacitor structure
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Author Bio:
Jianlong Tian received his B.S. degree in Mechanical and Electric Engineering from the Agricultural University of Hebei, Baoding, China, in 1989; and his M.S. degree in Detection Technology and Automatic Equipment from the Beijing University of Chemical Technology, Beijing, China, in 2003. He has been working towards his Ph.D. degree at the University of Auckland, Auckland, New Zealand, since 2012. For more than eight years he worked as an Electronic Engineer for a couple of companies in Beijing, China. His current research interest include the high frequency and resonant operation of IPT systems, voltage controlled variable capacitors and soft-switching DC-AC power converters. 
Dr. Aiguo Patrick Hu received his B.S. and M.S. degrees from Xian Jiaotong University, Xian, China, in 1985 and 1988, respectively; and his Ph.D. degree from the University of Auckland, Auckland, New Zealand, in 2001. He served as a Lecturer and as a Director of the China Italy Cooperative Technical Training Center in Xian, China, and as the General Manager of a technical development company. He stayed for a semester at the National University of Singapore (NUS), Singapore, as an Exchange Postdoctoral Research Fellow with funding from the Asian2000 Foundation. Patrick is a leading researcher in the field of wireless power technologies. He holds 15 patents in wireless/contactless power transfer and microcomputer control technologies, has published papers in more than 200 peer reviewed journal and conference proceedings and has over 2600 citations. He authored the first monograph on wireless inductive power transfer technology, and contributed 4 book chapters on inductive power transfer modeling/control as well as electrical machines. Patrick is currently with the Department of Electrical and Electronic Engineering, University of Auckland, Auckland, New Zealand. He is also the Head of Research of PowerbyProxi Ltd, as well as a Guest Professor of Chongqing University, Chongqing, China, and Taiyuan University of Technology, Taiyuan, China. He is a Senior Member of IEEE, a former Chairman of IEEE NZ Power Systems/Power Electronics Chapter, and the current Chairman of the NZ North Section. He served as Secretary/Treasurer of the NZ Chinese Scientists Association, and is now the Vice President. His current research interests include wireless/contactless power transfer systems, and the application of power electronics in renewable energy systems - Corresponding author: J. Tian Email: jtia983@aucklanduni.ac.nz
Abstract: This paper proposes a Voltage-controlled Variable Capacitor Structure (VVCS) to adjust the frequency of an autonomous push–pull converter. Unlike traditional switch mode capacitors or inductors where active switches are used, the equivalent capacitance of the VVCS varies with the on/off periods of a diode controlled by a DC voltage. The frequency of the autonomous push–pull converter can be controlled by this DC voltage when the VVCS is used as a variable resonant capacitor. As no active switching is involved in the VVCS, the circuit operates more smoothly than its switch mode counterpart so as to provide a simple way to adjust the operating frequency of the autonomous push–pull converter for high frequency and low electro magnetic interference operations. Mathematical model is developed for the relationship between the equivalent capacitance of the VVCS and the DC control voltage, and is verified by experimental results at more than 900 kHz with an approximately 12 W inductive power transfer system.
