DC-Link Voltage Reduction with Synergetic Common-Mode Voltage Control of Single-Phase Two-Stage Non-Isolated EV Chargers

As interest in climate issues grows, research on electric vehicles (EVs) and their charging technologies is advancing. Non-isolated topologies have been proposed to improve EV charger efficiency and power density. However, removing the galvanic isolation stage increases leakage currents, potentially causing electric shocks to users. These currents, generated by low-frequency (LF) common-mode voltage (CMV), are difficult to attenuate with EMI filters. Injecting LF CMV into the power converter can reduce leakage currents but requires higher DC-link voltage, increasing losses and reducing efficiency. This paper proposes a two-stage non-isolated EV charger with an AC/DC power factor correction (PFC) converter and a DC/DC three-level regulator. The PFC and regulator synergistically share the CMV to lower the DC-link voltage while maintaining leakage current reduction. The proposed method enables operation at lower DC-link voltage and higher modulation index (MI) regions. Experimental validation using a prototype confirms its effectiveness.