Common Mode Analysis of Non-Isolated Three-Phase EV-Charger for Bi-Directional Vehicle-to-Grid Operation

For future Vehicle-to-Grid (V2G) applications, the six-switch full-bridge is often used as AC-DC front-end converter of a three-phase EV-charger. In many publications, the common mode (CM) noise is not taken into account. However, this must not be neglected considering the large effective capacitance, of up to 3 muF, as allowed by new standards. In this paper, different modulation techniques are investigated, related to their CM-noise. Based on electric circuit simulations, CM-filters are estimated, and the CM-currents are investigated. Accordingly, the conventional six-switch full-bridge is practically difficult to use in non-isolated chargers, because the resulting CM-currents and/or the required EMI-filter become too large, even if CM-Voltage optimized modulation techniques are used.