Modular Three-phase Single-stage Isolated AC-DC Converter for Electrolytic Capacitor-less EV DC Charging

Abstract

This paper presents a three-phase AC-DC converter formed by three single-stage electrolytic capacitor-less isolated AC-DC modules. The parallel output connection of the three modules provides DC battery current despite the pulsating current of each module at twice the mains frequency. The two interleaved totem-pole circuits are switched at fixed 50% duty, resulting in a ripple-free sinusoidal grid current with very small filter inductors. The control is simple and easy to implement since the phase-shift angle is the only control variable. The proposed control is able to provide DC current under unbalanced conditions. ZVS turn-on of all switches is achieved in both directions of power flow. A 11kW prototype of the proposed converter achieved a volumetric power density of 5.5 kW/L (90.4 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ). The prototype demonstrates 96.3% peak efficiency and maintains relatively high efficiency over wide ranges of power and battery voltage.