An Adaptive EV Charger Based Reconfigurable Bidirectional Isolated DC-DC Converter with Wide Voltage Range of Operation

Abstract

The charging mode (pre-charging/CC-CV charging) has an impact on the efficiency of EV chargers. This is owing to the divergence of the soft-switching zone towards the hard-switching region, which is characterised by a wide range of power transfer and voltage conversion ratios. To make complete charging system unaffected over variety of EVs, this paper presents a three-phase bidirectional portable off-board EV charger compatible with a range of EVs. Here, three phase VSC is used for AC-DC active rectification while isolated DC-DC stage is used for charging control. It is configured with reconfigurable type isolated LLC resonating converter. The primary stage is controlled with SRF control while DC-DC stage is controlled based on the charging mode. Based on the mode selected (DAB, FB/HB-LLC), it is controlled with dual phase shift (DPS) control and frequency modulation, respectively. The mode selection is based on the optimized selection of current commutation path to secure optimum efficiency over complete charging profile. For reverse power transfer, DC-DC stage operates in dual active bridge (DAB) mode controlled with DPS control under CC discharging. Based on this, a detailed design approach is shown. For this, a 5 kW system is designed with 108-300 V EV batteries at different charging rates. A set of simulation results with wide range of battery voltages and charging rates show the soft-switching, peak current stress and grid to vehicle/vehicle to grid (G2V/V2G) performance of designed system.