A Multiple-Phase-Shift Control for a SiC-Based EV Charger to Optimize the Light-Load Efficiency, Current Stress, and Power Quality

An ac/dc + dual-active-bridge (DAB) circuit was found as one solution for the high-efficiency and high-power-density electric vehicle charger. One control option is to let ac/dc part only convert the grid voltage to a double-line-frequency folded sine wave, yielding near-zero switching loss of the ac/dc part and leaving the DAB stage to control both power factor and power delivery. Such a zero-to-peak input voltage and wide-range output voltage can obstruct the zero-voltage switching (ZVS) for the DAB stage, which is a must for high-efficiency applications even with SiC devices. While the conventional single-phase shift loses ZVS at light load, and the variable-switching-frequency dual phase shift (DPS) creates the grid-current distortion at the light load, this paper employs multiple-phase-shifts (MPS) control, which essentially is a fixed-switching-frequency triple-phase-shift (TPS) control at light-load conditions and jumping to DPS at medium-and heavy-load conditions. While the TPS control will sacrifice the system efficiency by introducing the circulating current, a multiobjective optimization is employed to optimize the current stress and efficiency simultaneously, using the database of the double-pulse-test result. Experimental results on a SiC-based charger validated the effectiveness of the proposed control algorithm, that is: 1) high efficiency(>97%) at heavy load (7.2 kW); 2) smooth sinusoidal current without bumps at zero-crossing points from the whole-load range; and 3) the smooth transition between the heavy load and light load.