High Misalignment Tolerance Wireless Power Transfer Systems

Wireless power transfer (WPT) technologies, including inductive power transfer (IPT) and capacitive power transfer (CPT), have gained significant popularity due to the their increased convenience compared to traditional wired power transfer methods. However, the unavoidable misalignment between the transmitter and receiver of WPT systems usually affects system operation, resulting in low output and efficiency. Hence, to increase the application of wireless charging in the future, the misalignment issues should be addressed.This thesis project aims to enhance the misalignment tolerance of wireless powertransfer systems through innovative coupler mechanism designs and the implementation of advanced control strategies. Additionally, the project seeks to improve overall system performance through mathematical model-based optimization.The initial focus of this work is on a CPT system, which is targeted for consumer electronics applications. To mitigate the misalignment problem, a novel capacitive coupler is designed, ensuring a constant overlap area and consistent coupling capacitance between pairs of coupling plates. Then, analytical models for coupling capacitance and resistance of this proposed coupler are developed to optimize coupler’s parameters andthe choice of dielectric materials. As a proof of concept, a 20-W prototype featuring the proposed capacitive coupler is constructed, achieving 100% lateral misalignment tolerance in both the x and y axes, equal to 100% coverage of the transmitter region,and a±75◦rotational tolerance. For the IPT system, a homogeneous transmitter coil is introduced to create a uniform magnetic field, resulting in constant mutual inductance. Utilizing Biot-Savart’s law, magnetic field, inductance, and mutual inductance of the inductive coupler are mathematically modeled. These models are then combined with an algorithm to optimize the parameters of the homogeneous transmitter coil. Furthermore, the coil’s resistance is derived and integrated into a circuit model for system optimizations. As a result, a 200-W 6.78-MHz IPT system is developed, achieving a peak efficiency of89%. The system also demonstrates a misalignment tolerance of 34.7%, allowing for the utilization of 67.10% of the transmitter region. Despite the advantages of the homogeneous transmitter coil in improving misalignment tolerance, approximately 33% of transmitter regions is still not being utilized. To further enhance performance, control strategies are incorporated. Parity-time (PT) symmetry-based control is proved to be effective in this regard. In this study, a PT-symmetry-based IPT system with a homogeneous transmitter coil is showcased, achieving 100% misalignment tolerance. With the homogeneous transmitter coil, the circuit operates in a fixed-frequency mode when the receiver is within the homogeneous area, leading to soft switching and increased efficiency. Additionally, the impact of controller delay on the system performance is analyzed, revealing that such a delay results in the circuit operating at a lower frequency than the desired resonant frequency, exacerbating hard switching and increasing losses. To address this delay issue, a compensation network is designed and implemented in both analog and digital controllers.