Advanced wireless power conversion technologies : topology, modulation, and control

Abstract

There is an increasing number of emerging applications adopting wireless power transfer. In turn, these emerging applications impose new challenges and requirements to the existing wireless power transfer technology. This thesis aims to advance the state-of-the-art wireless power transfer technology via the development of advanced wireless power conversion technologies. Initially, the state-of-the-art wireless power transfer systems are assessed, from which new findings are identified. Theoretical studies and experimental verifications are performed to verify the origins and adverse effects of these new findings. Also, new challenges that arose from the findings motivate the development of new topologies, modulation schemes, and control methods. Experimental results are provided, and comparative studies are conducted to verify the effectiveness and feasibility of the proposed solutions. The major contributions of this thesis include: 1. The phenomenon of beat frequency oscillation in two-stage wireless power receiver systems is discovered and modelled. Design recommendations to alleviate or eliminate the oscillation are provided. 2. The right-half-plane zeros of the buck converter used in two-stage wireless power receiver systems are discovered and quantitatively described. The origin and adverse effects of the right-half-plane zeros are discussed and experimentally verified. 3. Phase-shift modulated resonant topologies (class E and differential class E resonant inverters/rectifiers) are developed to enable the single-stage AC-DC conversion and power flow control. In addition, owing to the use of phase-shift modulation in its control, bidirectional operation of the resonant topologies (as wireless power transceivers) is feasible. 4. Hybrid modulation schemes that integrate phase-shift modulation and pulse width modulation are developed for single-stage wireless power receivers. With the hybrid modulation schemes, soft switching operation and output regulation are enabled concurrently such that efficiency and controllability of the receivers are improved. 5. It is found that the dynamic response and stability margin of two-stage wireless power receiver systems are adversely affected by their inherent right-half-plane zeros. Topologies modifications are performed on the two-stage wireless power receiver systems to eliminate the right-half-plane zeros and therefore improve the dynamic response and stability margin. 6. The transmitter-side current overshoot is attributed to the closed-loop right-half-plane zeros of the two-stage wireless power receiver. A control method is developed to increase the frequency of the closed-loop right-half-plane zero. Our work shows that by increasing the frequency of the closed-loop right-half-plane zero, the dynamic response is improved, and the transmitter-side current overshoot is suppressed. This thesis contains three parts. The first part (Chapter 1 and 2) gives the background information and delivers an overview of the wireless power conversion technologies. Subsequently, the second part (Chapter 3 and 4) reports the new findings. The third part (Chapter 5 to 12) presents various advanced solutions to address the new challenges arose from the new findings. Finally, the last chapter (Chapter 13) concludes the thesis and suggests some future works.