Soft-switched, active-clamped DC/AC and AC/AC converters for IPT-based wireless charging applications

Abstract

The acquisition of inductive power transfer (IPT) technology in commercial electric vehicles (EVs) alleviates the inherent burdens of high cost, limited driving range, and long charging time. In EV wireless charging systems using IPT technology, power electronic converters play a vital role to reduce the size and cost, as well as to maximize the efficiency of the overall system. Conventionally, the IPT systems utilize two power conversion stages to generate a high-frequency primary current/voltage from low-frequency utility supply, causing the lower power density and higher cost of the system. Recent research shows that the use of direct AC/AC converters in the IPT systems can mitigate these limitations. However, these topologies still have the drawbacks such as large switching component count, poor input current quality, or complex control schemes. In this thesis, a novel direct AC/AC active-clamped half-bridge (HB) converter for the wireless EV IPT charging application is proposed and implemented. The proposed converter can overcome the aforementioned limitations of the existing power converter topologies. It offers several appealing features such as high efficiency, less component requirement, continuous sinusoidal input current, and zero voltage switching (ZVS) operation. Moreover, a new simple hybrid (nonlinear and linear) dual-loop control strategy for the AC/AC active-clamped HB converter based IPT charging system is developed. It enables the input current correction and charging current regulation in a single power conversion stage. The performance of the proposed charging system is verified by simulation and experimental results on a 1.0-kW prototype. The experimental verification shows that the proposed IPT system with a peak overall efficiency of 93.4 % is more efficient than the existing single-stage converter based IPT systems. In order to have a knowledge foundation for the successful analysis, design and implementation of the proposed AC/AC converter system, an active-clamped half-bridge boost inverter (HBBI) based IPT charging system is initially studied. The ZVS operation principles, mathematical model, design methodology, and control strategy of the active-clamped HBBI based system are derived and developed in detail. Simulation and experimental results are given to verify the theoretical analyses and system performance.