A Primary Shunt Inductor Compensated Inductive Power Transfer System with Natural ZVS for Battery Charging Application

Inductive power transfer (IPT) technology is suitable for battery charging applications due to its advantages of safety, convenience and weather proof. A primary shunt inductor compensation topology (named as L-S/S) is proposed in this paper to achieve a target constant current (CC) and constant voltage (CV) battery charging profile with natural zero voltage switching (ZVS). The design and analysis of L-S/S compensation are based on the characteristics of the gyrator as it provides a simple way to analyze the resonant circuits. Load-independent CV outputs and CC outputs can be achieved at two different operating frequencies, respectively. Zero phase angle (ZPA) can be maintained at these two operating frequencies to eliminate the reactive power. Since the shunt inductor of the primary side naturally provides a turn-off current, ZVS can be achieved at the exact resonance point without other assisted methods such as slightly adjusting the resonant parameters. Experiments are carried out on a 1kW prototype to prove the proposed method. Experimental results show that ZVS is naturally realized in various charging states. The current fluctuation is less than 1% in CC mode, and the voltage fluctuation is less than 4% in CV mode. Steady outputs can be achieved by slightly modulating the operating frequency. The peak efficiency is 95.2% at rated power.