Modular Soft-Switched EV Charger with Four-Leg PFC Stage and Transformerless On-Demand DC/DC Configuration

A modular soft-switched EV charger formed by a four-leg AC/DC converter, which acts as PFC stage, and a non-isolated DC/DC converter that manages the interaction between the DC link and the battery, is presented in this paper. The analyzed device leverages existing three-phase topologies by extending it to work also in a four-wire configuration, allowing to control the neutral conductor current. The control algorithm is performed through the usage of an extended Clarke-Park transformation, which exploits the common and differential mode signal decomposition to separate the neutral current control and the regulation of the common mode voltage. Moreover, differential and common mode signals are also used in the battery-side converter to control the charging/discharging operations of the battery and to stabilize the common mode voltage. Furthermore, a discrete Variable Frequency Critical Soft Switching (VFCSS) technique is used to boost the efficiency of the EV charger by maintaining soft-switching operation both on the grid side and on the DC side. The proposed topology and control scheme are verified through a simulated model in PLECS/Simulink. Simulation results have been reported for both charging and discharging operations. In particular, constant current discharging has been simulated under either balanced or unbalanced three-phase scenarios, showing the effectiveness of the proposed control scheme.