Design of Transformerless Electric Vehicle Charger with Symmetric AC and DC Interfaces

This paper focuses on the transformerless fast charging solution of plug-in electric vehicles (PEV). In a PEV system, the chargers can be classified into three levels: ac level 1 (< 1.92 kW), ac level 2 (< 19.2 kW), dc level 3 (>19.2 kW) [1]. For the high-power level 3 fast charging system, it is not viable to place an on-board charger due to the volume and weight. We propose two topologies for off-board non-isolated DC charger to provide fast DC charging with high-power (up to 22 kW). The proposed topology includes two stages, AC/DC rectifier and DC/DC converter. According to the grid requirement, the AC/DC rectifier topologies can be divided into single-phase and three-phase applications. For the three-phase grid interface, the design of the DC charger uses the same hardware for both the grid interface and the DC/DC stage. The development and manufacturing costs are reduced due to the symmetric design of the two stages of circuit. The leakage current issue of the non-isolated system is solved based on the proposed topologies and the volume and weight are largely decreased because of the transformerless structure. The design procedures and a typical three-phase prototype are shown in this paper to verify the proposed structures.