Medium Voltage AC to Isolated Multiport DC Converter for Electric Vehicle Fast-Charging Stations

The dc fast charging stations operate at megawatt-scale power levels, drawing energy from the medium voltage ac (MVAC) grid to reduce transmission losses. It also requires local energy storage and the capability for renewable integration to reduce the load on the grid. Conventional solutions use a bulky line frequency transformer (LFT) to step down MVAC to low voltage ac (LVAC), followed by multiple ac–dc and isolated dc–dc converters, leading to lower efficiency especially during power flow between local storage and electric vehicles. Existing multiport MVAC-to-LVDC converters often rely on modular multilevel converters (MMCs), which has higher component count, or cascaded H-bridge (CHB) solutions with additional battery storage and additional bridges for power exchange. This article proposes a novel CHB-based multiport topology that eliminates the need for additional battery storage, additional semiconductor devices, and additional MV-insulated transformer winding compared to an MVAC to single port LVDC converter. The proposed modulation and control strategy ensures the independent operation of each LVDC port, and unity power factor (UPF) operation at the grid interface. A step-by-step design for an 11 kV two-port converter is presented, and experimental validation is performed using a 1.2 kW laboratory-scale prototype with an efficiency of 95.3% at rated load.