| More and more energy and environment problems simulate the rapid development of electric vehicles (EV). On-board charger, as a key component of electric vehicles, has become a hot research topic. Designing high performance on-board charger, with high efficiency, high power factor, high reliability, plays an important role in promoting healthy development of EV industry. In this paper, the research mainly focuses on the electrical part of a 3.3kW digital control on-board charger.First of all, a preferred two-stage circuit topology is proposed based on the suvey of the existing solutions and techniques. It includes a bridgeless Boost PFC converter followed by an isolated full-bridge LLC resonant DC/DC converter with parallel-series connected transformers.In second chapter, the design method and results of key components are presented after analyzing the operation principle of bridgeless PFC converter. An optimization design method of PFC inductor is proposed. Experimental result verifies the accuracy of the detailed loss analysis on power circuit. PFC inductor with large current shows obvious nonlinear characteristic. Inductor nonlinearity seriously limited the bandwith of inner current control loop and badly affects control stability. And then the mechanism and consequences are theoretically analyzed. The optimal design considerations of PI parameters are summarized at last.The paper, in the third chapter, presents a full-bridge LLC resonant DC/DC converter with parallel-series connected transformers used for wide output voltage range and high power density applications. The circuit operation principle and characteristics are analyzed in detail. The power self-balance between two transformers and soft switching performance are verified by experiment. A practical optimization design method of the resonant parameters is proposed for wide output-voltage charging requirements. Optimization mathematical model is built and general design steps are summarized. Simulation and experimental results verify the effectiveness of the above method. Then, design results of key power components, loss analysis and control strategyies are sequentially presented.Finally, a prototype, which achieves a peak efficiency 96% and full-load efficiency 95% at 220Vac input, is presented and the detailed test results are analyzed. The prototype demonstrates high performance including high efficiency, high power factor, wide output voltage. The effectiveness of the proposed design is fully verified. |
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