High power density Z-source resonant wireless charger with line frequency sinusoidal charging

Abstract

Wireless charger for Electric Vehicles (EVs) is an off-line application and it needs power factor correction (PFC) function, which usually consists of a front-end boost PFC and a cascaded DC/DC converter. Z-source resonant converter (ZSRC), a single-stage solution with low cost and high efficiency, was proposed for EV wireless charger lately. The Z-source capacitors in the ZSRC are designed to absorb the double line frequency ripple in this single-phase application. Sinusoidal charging, which allows the double line frequency ripple to propagate to the output, is another solution aiming at reducing the bulky capacitors. Recently, a comparison of low frequency (120 Hz) sinusoidal charging and DC charging shows negligible impact on Li-ion batteries' performance. Therefore, ZSRC's capacitor, the biggest component, can be reduced dramatically from millifarad to several microfarads with sinusoidal charging technique, which features the ZSRC high power density. Also, it keeps the Z-source's benefit of boost ability and being immune to shoot-through problems. In this paper, the sinusoidal charging behavior for the ZSRC is modeled, and a control scheme that has both PFC function and load regulation for sinusoidal charging is proposed. It can pass IEC61000-3-2 Class A criterion. Experimental results based on a 1-kW prototype with 20-cm air gap between the primary and secondary side are presented to illustrate the proposed control scheme.