Three-Phase Bidirectional Ultra-Wide Output Voltage Range Current DC-Link AC/DC Buck-Boost Converter

High power EV chargers connected to AC power distribution architectures employ a three-phase (3-Φ) PFC rectifier front-end and a series-connected isolated DC/DC converter to cover a wide range of traction battery voltages and efficiently supply the required charging current. In this paper, the operating principle of a two-stage 3-Φ buck-boost current DC-link PFC rectifier system is first introduced. Its optimal operating modes, minimizing conduction losses, switching losses, and CM noise emissions for every DC output voltage level, are identified. Adequate modulation strategies are proposed and explained through detailed switching patterns. Importantly, the two stages of the PFC rectifier system, i.e. the 3-Φ buck-type current source rectifier input stage and the subsequent three-level boost DC/DC stage, are controlled synergetically which ensures an automatic selection and seamless transition between the optimal combinations of operating modes of both stages. Simulation results verify the operation of the described power converter for different output voltage and output power levels. Furthermore, a new common-mode (CM) filtering method, requiring a CM DC-link inductor and a capacitive connection between an artificial 3-Φ neutral point and the DC output mid-point, is analyzed with the support of a derived CM equivalent circuit. Finally, a complete guideline for the design of the CM filter, based on analytical calculations of the CM voltage-time area, is presented.