An Investigation On On-Off Keying , Soft-start And PFC Modulation Techniques Of Wireless Power Transfer Systems

Wireless power transfer technology can realize convenient and safe wireless charging of electric vehicles,which is the key technology to promote the popularization of electric vehicles.Efficiency and cost are the core indicators of wireless power transfer systems.To achieve high efficiency operation,traditional wireless power transfer systems rely on additional converters and sophisticated control methods.This dissertation mainly studies the method of improving the efficiency of the wireless power transfer systems from the perspective of the modulation of the primary-and secondary-side switch signal.In this dissertation,the On-Off keying modulation technology of wireless charging system for electric vehicles is studied.The requirements of this technology on the output filter capacitance of the system are analyzed.The expression of the duty cycle of the modulation signal is deduced when the coupling coefficient and the load resistance change.And it is proved that the modulation of the duty cycle can simultaneously satisfy the output power adjustment and the highest efficiency operation.Experimental verification was carried out on a 3.3kW experimental platform.The results show that compared with the phase-shift control method,the On-Off Keying modulation technology can significantly improve the overall efficiency of the system.A large current overshoot occurs when the wireless power transfer system is started.This is the key problem that needs to be solved when applying On-Off Keying modulation technology.Based on the transient analysis of the wireless power transfer system during the start-up phase,this dissertation proposes a method for achieving fast soft-start of the wireless power transfer system,which can suppress the current overshoot during start-up and ensure that the the system enters the steady state fastest.The proposed method was verified on a 3.3kW experimental prototype.Based on the dual active full-bridge wireless power transfer systems,thisdissertation proposes a method to achieve power factor correction(PFC)by modulating the secondary-side active rectifier.This method can replace the PFC converter located at the front end of the primary inverter,and achieve the purpose of simplifying the system and reducing costs.A prototype of a 1kW wireless power transfer system was built to verify the proposed method.