Transformer Isolated Fault Tolerant Three Phase Active Front End Converter for EV Charging

An electric vehicle (EV) charging scheme is proposed using a transformer isolated three-phase four-wire two level pulsewidth modulated (PWM) fault-tolerant active front-end converter (AFEC) followed by dc-dc converters for charge control. The AFEC is controlled to exhibit fault-tolerant operation with balanced three-phase supply line currents at unity displacement factor (DF) in the event of zero current in one line of the converter. While existing fault-tolerant schemes incorporate additional hardware switchover in the form of the redundant leg for the open circuit fault of one phase, the proposed scheme can maintain balanced supply line current at unity DF using a modified control scheme without any additional hardware during an open circuit failure of either a leg of AFEC, line reactor, connecting cable, or one secondary phase of transformer. The proposed scheme uses a method of readjusting the phase positions of the converter-controlled line currents using the Delta(Delta)-Star (Y) isolation transformer. The scheme can be conveniently used to enhance fault tolerant capability of EV charging stations. Simulation and experimental results validate the effectiveness of the proposed scheme.