Zero Sequence Voltage Control Enabling Transformerless Electric Vehicle Chargers

The transformer is one of the most bulky, expensive and lowest efficiency components in a typical electric vehicle charging system. Its removal is conducive to enabling greater proliferation of charging infrastructure and the adoption of electrified vehicles. However, simply removing it can lead to common mode voltage and leakage current issues that present a safety hazard. To address this and to be compliant with international standards, a transformerless electric vehicle charging system enabled by control is proposed without need for additional components. This is achieved by connecting the three-phase filter capacitor neutral point to the DC negative, which allows the zero sequence voltage to be controlled, thereby mitigating leakage currents. Simulations show that the leakage current of the proposed transformerless charger can be made standard compliant with the topology while experiments provide validation through zero sequence voltage and active and reactive power steps. The results demonstrate that the transformer can be removed from electric vehicle chargers.