High power factor Z-source resonant wireless charger with soft switching

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. Recently, Z-source resonant converter (ZSRC), a single-stage solution with low cost and high efficiency, was proposed for EV wireless charger. Combining with the Z-source network, the control scheme is more challenged and sophisticated. Traditional phase-shift control and pulse notch control have been applied to ZSRC performing PFC function and load regulation successfully. However, both aforementioned control schemes have hard switching characteristic which cannot be avoided when chopping the current for load regulation. The ZSRC has efficiency benefit over traditional two-stage structure in a narrow design window due to the large portion of switching loss. Hence, this paper presents a burst control method specific for ZSRC with soft switching. It can pass IEC61000-3-2 Class A criterion with double line frequency power absorbed in the Z-source network. The efficiency improvement is over 10% at half load. 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.