Zero-Leakage-Current Zero-Common-Mode Modulation for Neutral-Point Connected Three-Phase Non-Isolated On-Board Chargers

The power electronics in electric vehicles are moving towards very high efficiency and even higher power densities. In order to push the boundaries further, one research trend for on-board chargers is to remove the isolation transformer in order to save losses, size and cost. However, non-isolated chargers require sophisticated system design and control to limit leakage and touch currents to very stringent levels of only a few mA. In this paper, a novel modulation scheme eliminating the leakage current through the parasitic capacitances of the HV battery is proposed for three-phase neutral-point connected rectifiers/inverters. The effectiveness and performance of the proposal is validated by means of simulation and also by experimental results based on an industrial 20-kW grid-connected NPC inverter with digital control.