Research On Contactless Bidirectional Resonant Converter In Emergency Charging For Electric Vehicles

With the energy and environment problem getting worse, Electric Vehicle (EV) is paid muchattention because of its clean and environmental advantage. The power battery provides storgedenergy to EV while working, but the power battery limits the development of EV. Therefore, the safe,reliable, and cost effective charging technology for the power battery become the key technique.Currently, there are three types of solutions for EV power battery charging: conduction power supply,battery replacement, and wireless power supply. By utilizing the technology of Wireless PowerTransmission (WPT), EV can get energy complement even when it is travelling on road, and it canreduce the requirement for power battery capacity. Besides, compared with the traditional chargingmethod, WPT is safer and more convenient.The WPT for EV consists of driving charging and parking charging. The emergency power supplysystem by WPT when power of EV runs out is suggested in this thesis. Two parallel windings connectthe power batteries of two EVs, and the power can flow in two directions. Therefore, the contactlessbidirectional converter is main circuit in this thesis.The contactless bidirectional converter is divided into three stages in this thesis. Firstly, theequivalent model of two cascaded contactless transformers is given, and this model simplies thetransformer parameters. Secondly, by comparing the different compensation methods of contactlesstransformers, the appropriate compensation method is chosen. According to the generation method ofbidirectional converter, the inverter circuits are selected. Finally, the series-series compension doublefull bridge contactless bidirectional resonant converter is adopted as the main circuit.There are variable control methods for double full bridge contactless bidirectional resonantconverter due to the eight numbers of the switches in the topology. This thesis analyzes the controlstrategy for contactless bidirectional resonant converter in emergency charging，PLL+PWM controlon supply-side and two new control strategies are proposed, one is PLL control on supply-side andPWM control on receiving side, the other is fixed-frequency on supply-side and PWM control onreceiving side. And the former one has the difficulty in system control, since PLL loop and PWM loopare coupling.A1800W contactless bidirectional resonant converter prototype is fabricated. The contactlesstransformer is simulated with ansoft Maxwell3D. The output voltage curve is given and comparedwith calculated curve. Under PLL+PWM control strategy, the converter efficiency at1800W output can reach72.5%. Under PWM control strategy on receving-side, the converter efficiency at1800Woutput can reach77%.