Common Mode Analysis of Non-Isolated Integrated Chargers based on NPC Inverter for Electric Vehicles

Non-isolated integrated chargers take advantage of the electric vehicle’s on-board power electronic for charging purposes: the traction drive inverter is a good candidate to be used in the battery charging process, while the stator windings of the electrical traction motor can be utilized as static inductors. In a typical non-isolated three-phase grid-connected system, there exist a leakage current flowing through the common mode (CM) parasitic path between the vehicle’s chassis and the DC ground. Large leakage current lead to potential electric shocks to the end-users, as well as on-board electronics failures. In this paper, a 3-level Active Neutral Point Clamped (ANPC) inverter is used together with the stator windings of a permanent magnet synchronous machines (PMSM) for charging purposes. The issue of CM leakage current through the parasitic path is analysed for different earthing systems. Different modulation techniques are critically compared in terms of effectiveness in reducing the leakage current, grid currents distortion and capability in reducing the DC current ripple during battery charging. Simulation results are provided in support of the analysis.