Research on topology and control of inductive charging

Abstract

The acceleration of electric vehicle (EV) adoption necessitates the development of charging technologies to alleviate range anxiety, primarily resulting from insufficient charging infrastructure rather than inadequate battery capacity. Inductive charging, offering convenience, safety, and efficient space utilization, emerges as a promising solution. Therefore, in-depth research on topology and control of inductive charging systems is conducted in this thesis. A comprehensive analysis of fundamental and higher-order compensation network topologies has been undertaken to facilitate inductive power transfer (IPT) circuit design. Notably, a comparative evaluation is conducted between the double-sided LCC (Inductor-Capacitor-Capacitor) compensation network and the SS (Series-Series) compensation network. Furthermore, a novel reconfigurable compensation topology, adjusted by switches integrated in the compensation circuit, is proposed, enabling the realization of constant current (CC) and constant voltage (CV) outputs. While compensation networks contribute to high efficiency and stable output in IPT systems, they may not fully meet the rigorous requirements for power regulation and soft switching. Therefore, the implementation of control methods becomes imperative. The precondition of applying effective control strategies hinges on accurate acquisition of system parameters, particularly for the coupling coefficient and load resistance. To fulfill this requirement, an artificial neural network (ANN) methodology is employed to estimate the coupling coefficient. Moreover, a simplified system model is developed to calculate the load resistance of the remote receiver. Compared to conventional approaches, this methodology offers an alternative means of estimating mutual inductance and load resistance using primary-side information exclusively. Achieving zero-voltage switching (ZVS) and maintaining a constant output in an IPT system are paramount, as ZVS is essential for optimizing operational efficiency, while a constant output is indispensable to meet battery specifications. Simultaneous attainment of zero-voltage switching (ZVS) and constant current/constant voltage (CC/CV) battery charging in an IPT system necessitates the employment of two control variables. The responsibility of output regulation lies with phase-shift control, while the implementation of self-oscillating control facilitates soft switching, thereby minimizing switching losses. The hybrid control strategy outperforms the standalone variable frequency control. To regulate the output power in an inductive battery charging system without loss of ZVS, a novel sub-harmonics switching technique called bi-frequency pulse-train (BF-PT) control is introduced. BF-PT control employs a combination of high- and low-frequency pulse trains, which are evenly distributed to mitigate variations in the winding current. By dynamically adjusting the ratio of distinct pulses, the output power can be effectively enhanced or reduced as required. The power-split concept is introduced as an innovative approach to minimize power processing stages in the system. In this proposed design, a novel receiver circuit is developed, dividing the secondary side into two separate channels. The primary channel directly supplies the majority of power to the load, while the secondary channel utilizes a low-voltage, low-power DC-DC converter to regulate the output voltage. By implementing this design, both the voltage stress on the components and the number of power processing stages are reduced, resulting in improved efficiency and performance. Finally, theoretical analyses, system simulations, and prototype experiments are conducted to validate the proposed concepts and methodologies, providing substantial evidence of their efficacy and practical feasibility.