Virtual Synchronous Machine Based Direct Charging Power Control for the Two-Stage EV Battery Charger

In this paper, a direct charging power control strategy (DCPC) based on virtual synchronous machine (VSM) technique is proposed for the two-stage EV battery charger. In the proposed solution, the two-stage charger involves a three-phase full bridge-based AC-DC stage and a buck/boost DC-DC stage. In control of the front-end AC-DC stage, the core algorithm of the traditional VSM is adopted. Nevertheless, unlike the traditional VSM-based battery charging scheme, the DC-bus closed-loop in the traditional VSM algorithm is replaced by a positive feedback-based DC power compensation loop, and meanwhile, the DC-bus voltage is regulated by the rear stage DC-DC converter. The proposed method can ensure stable DC-bus voltage control and direct control of charging power. Due to the existence of power compensation control, the power balance between AC and DC terminals can be indirectly controlled without complex power losses calculation process. In addition, the autonomous AC frequency and voltage regulation abilities of the VSM technique can be inherited in the proposed method, which can appear a grid-friendly charging pattern to ensure more stable battery charging. To verify the validity of the proposed method, systematic analysis and experiments are performed on a developed test bed.