Electric Vehicle Charging System Utilizing a Transformerless Common Mode Voltage Suppression Technique

With the increasing adoption of electric vehicles (EVs) globally, there is a growing need for more public charging infrastructures, which demands compact designs to minimize their cumulative footprint. Since transformers are key contributors to the overall cost, size, and power losses in charging systems, integrating non-isolated AC-DC and DC-DC converters can potentially result in more economical, compact, and efficient EV chargers. Nevertheless, in the absence of galvanic isolation which is usually provided by isolation transformers, alternative strategies are needed for safety purpose and to mitigate common mode (CM) or ground leakage currents. This article proposes a three-phase transformerless battery charger with buck-boost functionality that significantly reduces ground leakage currents. It features a two-stage conversion architecture: a three-phase front-end T-type converter employing a modified vector modulation and a back-end bidirectional four-switch buck-boost (FSBB) converter operated with a symmetric switching scheme. Collectively, this circuit and its modulation strategies for the active devices produce a low high-frequency CM voltage. This simplifies the filtering requirements for grid and safety compliance while efficiently managing various battery charging profiles. The proposed system and advantages on ground leakage current attenuation is validated through extensive simulations in PLECS and LTSPICE and with a SiC-based experimental demonstrator. The demonstrator shows a significant reduction in leakage current compared to conventional SVPWM in the front-end, along with a synchronous switching scheme in the back-end circuit.