A Multistage Constant-Current Wireless Charging Method Using Pulse Frequency Modulation for Multistorey EV Carparks

For the wireless charging system in multistorey electric vehicle carparks, this paper proposes a multistage constant-current (MSCC) charging method using the pulse frequency modulation (PFM) for series–series inductive wireless power transfer. The proposed system has the advantages of fast charging, wide-range zero voltage switching (ZVS), low control complexity, and less charging harmonics. In addition, the PFM-MSCC charging process offers reduced switching frequency and reduced switching losses while avoiding the use of additional DC-DC converters, thus allowing for a significant improvement in efficiency. A new equivalent circuit model based on lithiumion batteries is developed for verification. Finally, the ZVS and zero phase angle operations can be readily realized, and the system efficiency of the whole charging process can reach up to 94.5%. Both theoretical analysis and results verify the feasibility and effectiveness of the proposed PFM-MSCC control strategy.