Game-Changing SiC-Based Reference Design for EV Charging

Electric vehicles (EVs) are now a major focus for power electronics endeavour, with a large proportion of engineers involved in finding ways to improve their performance and extend their range. Alongside this, there is a great deal of activity in respect to developing next generation charging infrastructure to support these vehicles. To address the need for additional engineering assistance in EV charging system development, Toshiba has introduced the RD044-DGUIDE-01 reference design.

This 3-phase 400VAC reference design is well suited to the demands of EV charging infrastructure implementations. It leverages the latest innovations in wide bandgap power discretes. Requiring the allocation of only minimal engineering resources, it enables advanced charging station designs (with elevated conversion efficiencies) to be undertaken.

Key to the reference design’s high conversion efficiency figures is the switching technology that it relies on. Though IGBTs are generally used in high-voltage switching applications, they have inherent losses associated with them - which substantially impact upon the efficiency levels that can be attained. Furthermore, the switching speeds that they will reach are not that high. This, once again, has efficiency implications. By using a silicon-carbide (SiC) MOSFET instead - namely a Toshiba TW070J120B N-channel device - the high-voltage operation required can still be supported by the RD044-DGUIDE-01, but without the relatively heavy switching losses that an IGBT-based approach would lead to. With a 1200V-rated withstand voltage and an operational temperature range going all the way to 175°C, the TW070J120B is robust enough to deal with harsh automotive environments. This SiC MOSFET has a 70mΩ on-resistance, which lowers the conduction losses witnessed considerably. It can deliver conversion efficiencies of 97% and supports 50kHz switching frequencies. Using this device has other notable benefits. It allows for a downsizing in the accompanying passive components, thereby saving board space and reducing overall costs.

Though EV uptake is still relatively low, the greater prevalence of charging points will help to encourage more drivers to swap from internal combustion engine cars to their more environmentally friendly counterparts. The charging technology could have a role to play in incentivising this change over too. One possible use case that could make the purchasing of EVs more attractive is the potential for their batteries to be used as a means for the owner to generate revenue. Through bi-directional charging, electricity storage reserves connected to the mains supply could be used to help with load balancing during periods of high demand. This is something that will become increasingly important to electricity distribution as society becomes more reliant on renewable energy sources, which are by definition more prone to fluctuations.  

Toshiba’s RD044-DGUIDE-01 reference design is described in the following free to download white paper