To achieve high power density, and high efficiency in EV charging station applications, in this paper, a three-phase with three single-phase single-stage ac-dc converters based on LLC resonant converter with variable switching frequency and variable delay-time control is proposed. With the proposed control, only one control variable, either the switching frequency or the delay-time, is controlled at a particular instant during ac line cycle in order to shape the input current to achieve PFC. The proposed topology and control ensure ZVS turn-on of switches while also limiting the switching frequency variation range in wide input/output voltage range. The detailed block-diagram of control is provided. Finally, the experimental waveforms for 10kW single-phase single-stage ac-dc converter are provided. At full-load operation, at VAC = 480Vrms, VO = 400V, measured efficiencies of 97.17% and 97.3% and measured iTHD of 3.04% and 4.47% are achieved at PO = 9.85 kW and PO = 6.59kW, respectively.
