Rapid Electric Vehicle Charging Based on Silicon Carbide Enabled Medium Voltage DC Tranmission Systems

Rapid electric vehicle (EV) chargers with power ratings above 100 kW will become more common in the future. Reinforcing UK distribution networks with additional power handling capacity can be costly and disruptive. This is due to the limited headroom in 11 kV distribution networks and the high population densities where 11 kV/400 V transformers are located. This paper proposes a medium voltage DC (MVDC) system that bypasses the 33 kV/11 and 11 kV/400 V AC transformers by transmitting 54 kV DC power directly to the EV charging stations. The 33 kV AC to 54 kV rectification in this system is proposed to be done by using a 29-level modular multilevel converter (MMC) implemented in 3.3 kV SiC MOSFETs. On the EV side, there will be a 54 kV to 800 V/400 V fully isolated DC/DC converter implemented with 3.3 kV SiC MOSFETs on the primary side and 1.2 kV SiC MOSFETs or Schottky diodes on the secondary side. This paper presents experimentally calibrated converter simulation results demonstrating improved performance in the MVDC system and shows this is only possible with SiC MOSFET technology, as the losses using silicon IGBTs make the system less efficient than the existing AC transmission system.