Evaluation of three-phase neutral-point-clamped PFC rectifier implemented with isolated DC-DC converters for EV fast charger

Abstract

In this study, a three-phase AC/DC neutral point clamped (NPC) power factor corrected (PFC) multilevel converter for off-board chargers of Electric Vehicles (EVs) is evaluated. The rectifier analysis has been tested by extensive simulations in combination with isolated DC-DC converters. This rectifier provides unity input power factor and efficiency above 96% for DC fast chargers rated at power levels up to 100 kW. The voltage ripple is below 0.5% for 800 Volt DC voltage. The current ripple is below 0.1% for 125 Ampere DC current. When the EV fast charger is evaluated with both isolated DC-DC converters, the NPC rectifier has less than 1% THD. This multilevel converter is highly efficient in terms of capacitor voltage balancing. The system has a simple control structure and does not require an extra PFC circuit. The converter operation and design calculations are presented with simulation studies. The simulation results of the system evaluated for isolated DC-DC converters demonstrate the validity and flexibility of the proposed charging system.