SiC-Based Improved Neutral Legs With Reduced Capacitors for Three-Phase Four-Wire EV Chargers

An electric vehicle (EV) charger can operate in an autonomous mode to create its own grid by utilizing the EV batteries during grid blackouts. This requires three-phase four-wire inverters as the grid-side ac/dc port of the EV charger to supply unbalanced loads. Although silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) can be adopted to increase the power density of these inverters, the second-order ripples exhibited on the dc bus caused by unbalanced loads need to be mitigated by a large dc capacitance-increasing the size of inverters. In this article, an improved neutral leg for three-phase four-wire inverters is presented, which not only provides the neutral current for unbalanced loads, such as a conventional neutral leg, but also reduces the second-order ripples on the dc bus without the need for additional hardware components. Furthermore, it can reduce by 50% the dc capacitance compared to its conventional counterpart. A control strategy featuring power decoupling capability is included for the improved leg. It was built with SiC MOSFETs and experimentally assessed with a three-phase inverter, with results verifying its effectiveness. For completeness, the performance of the improved neutral leg is also evaluated through simulations in PLECS and compared to a conventional neutral leg.