Bidirectional Electric Vehicle Charger Control Design with Performance Improvement

Bidirectional Electric vehicle (EV) charging technology is becoming more important. The EV on-board charger consists of an AC-DC converter followed by a DC-DC converter. The bidirectional AC-DC Vienna and the DC-DC LLC resonant converters provide the Grid-to-Vehicle (G2V) and Vehicle-to-Grid (V2G) modes. The AC-DC and DC-DC converters are responsible for the grid current and DC bus voltage control respectively across battery voltage and power variation in both G2V and V2G modes. The Pulse Frequency Modulation (PFM) is widely used for the LLC converter. Employing the PFM strategy causes LLC saturation for an important operating zone lowering the EV charger performances. This paper proposes a hybrid control strategy for the bidirectional EV charger to ensure DC bus voltage and grid current control. In G2V mode, the PFM strategy with variable DC bus request is implemented when the LLC converter is saturated. While in V2G mode, the Phase Shift Modulation (PSM) strategy is applied in order to avoid the PFM limitation. Outside of the saturation zones, PFM strategy is still applied. The results highlight the advantage of the proposed control strategy in improving the charger efficiency and control performances in both G2V and V2G modes.