A modular method for high power charging design

Technologies such as vehicle-to-grid (V2G) and vehicle-to-home (V2H) where the battery in an electric vehicle (EV) returns power to the grid at times of high demand, or simply powers a home in an emergency are bringing challenges to designers of vehicle chargers.

Instead of simply operating to transfer grid power to the vehicle battery via fast DC charging, they must now be able to move energy from the vehicle in the opposite direction.

Topologies that lend themselves to forming a bi-directional PFC and DC/DC converter are totem pole style PFC, dual-active bridge (DAB) and LLC converters. However, constructing a 22kW charger using these topologies can be a complex issue.

Examining the topologies, they all contain input inductors, single bridge legs and output capacitors which would allow a modular approach to design to be taken.

Leveraging this idea, Toshiba has developed a Modular EV Charger Reference Design Concept – known as their ‘SiC Cube’.

The SiC Cube comprises seven PCBs with the inner three being closely stacked power switches/bridge legs. Sandwiching these are the inductor and capacitor boards. On board high-power connections are made via copper current rails. Monitoring the analogue signals and providing digital control is performed by a microcontroller board that traverses the other five boards, with the final board being a backplane for connectivity.

Overall, the design targets a 22kW output for each SiC Cube, based upon Toshiba’s third generation SiC MOSFETs, aiming at power efficiency of up to 99%, and a power factor of 0.99. The compact and innovative construction should result in a power density of 3kW/dm³ within the 140 × 140 × 210mm form factor.

For very high power applications (such as fast DC EV chargers), multiple SiC Cubes can be combined in a parallel configuration to deliver power levels up to 150kW.

As the design is modular, individual boards can be reused in the design of other applications like DC/DC converters or inverters thereby saving development time and reducing design risk.

Toshiba’s detailed white paper describing their SiC Cube is available here: