SiC-Based EV Charger for DC Bus Second-Order Ripple Reduction

An attractive dc/ac inverter for electric vehicle (EV) chargers is the three-phase four-wire inverter as it is able to handle unbalanced loads, supply neutral current, and provide balanced voltages. However, generation of second-order ripple on the dc bus is inevitable under the presence of unbalanced loads. To mitigate the magnitude of this ripple, conventional four-wire inverters require large and expensive capacitors in the neutral leg. To alleviate these issues, this paper presents a novel three-phase four-wire inverter based on silicon carbide MOSFETs. The topology is configured as a dc/dc buck converter for each phase leg and the neutral leg. Moreover, the capacitance of the neutral leg has been reduced by around eight times compared to that of the conventional neutral leg topology, in turn increasing the power density and reducing overall cost. By adopting a suitably designed control strategy, the proposed topology decreases the second-order ripple on the dc bus and provides neutral current when operating under unbalanced conditions.