Transformer-less Medium Voltage EV Chargers

Fast charging of electric vehicles is a key technology for widespread electrification of transportation. To enable fast charging extending to megawatt levels, a medium voltage grid connection is imperative. Although transformers can be salvaged for this connection, a transformer-less power electronic topology can provide a significant power density advantage. Current source rectifiers (CSR) can convert three-phase AC to DC with high power throughputs. In this paper, a new carrier based PWM technique with switch clamping is developed for CSR, however, switch rating is identified as a limitation for their use in grid connected fast chargers. To allow a transformer-less medium voltage grid connection, a modular AC-AC buck topology is developed. This topology reduces the required switch voltage rating and can be controlled to step down voltages which are more compatible with switch ratings. Furthermore, the use of three-phase AC-AC buck with current source and voltage source rectifiers is proposed.