Study of wireless power transfer in dynamic vehicular system and other applications

Abstract

This thesis mainly focuses on the study of vehicular dynamic wireless power transfer (WPT) systems. The power transfer is via the high-frequency magnetic coupling, which is a commonly applied technology in high power wireless charging system. This class of wireless charging systems has higher accessibility, flexibility and reliability than cabled charging systems. However, the dynamic wireless charging (DWC) system has low efficiency and robustness due to fluctuated coupling coefficient and load condition. Hence, various optimized designs and advanced control schemes are proposed in this thesis. The coupler is one of the key components in wireless charging systems. In this thesis, the calculation of the coupling coefficient and core loss is introduced. In addition, a core-less optimization algorithm is proposed and implemented in various commonly used couplers. A grid-side synchronized frequency control is proposed based on mutual inductance estimation. The accuracy of the estimation is proved to have lower than ± 5% error. The implementation of a synchronized frequency control for a DWC system is realized, and the constant current (CC) and constant voltage (CV) charging can be achieved without any communication between the primary and secondary sides. A user-end feedforward control for realizing high stability in the EV DWC system is proposed in this thesis. The principle of the proposed control results in damped overshoots and fast system response. The experiments are conducted by injecting different kinds of disturbance, to prove the effectiveness of the proposed control method. The overshoot in battery charging current can be damped up to 74.6%, and the settling time can be shortened by up to 50.6%, respectively. A modularized EV WPT system is proposed to generate energy in a large-scale field, such as public parking lot. A self-positioning-based optimal frequency control (SP-OFC) strategy is proposed for achieving high frequency operation. Experimental results show high interoperability of the system with two types of Rxs, and the ZPA is achieved with high accuracy. By applying the optimal frequency control, the efficiency of the system can be improved by up to 14%. A speed and position sensor for a rotating motor is proposed based on WPT technology, which has the advantages of low cost and small size. The sensor integrates the wireless power supply function thus improving energy density. The maximum speed measurement error of the proposed sensor is 1.16%, and the maximum position measurement error is 2.24%. It can achieve 0.3W~0.5W wireless power transmission with around 48% efficiency. This function can effectively use the generated electromagnetic field energy to supply power to some coaxial sensors on the motor side. In conclusion, this thesis contributes to an optimization algorithm for the physical structure of the EV WPT system and the control method for both the primary and secondary sides. The heart of the proposed WPT systems is that they are all communication-free, simple in structures and control schemes, and have high reliability. Furthermore, another extended application of WPT are introduced. The bench markings are presented in the comparison studies in every chapter, which verifies the advancement of the thesis.