A different way to design high power charging solutions

Due to a combination of consumer demand and governmental policy to halt sales of new internal combustion engines (including in hybrid vehicles), all-electric battery electric vehicles (BEVs) are the future of personal mobility. In order to provide the performance and range needed to be successful a reliable, robust and efficient conversion of electrical energy is needed, especially for traction inverters and battery chargers.

Even though there are significant areas of similarity in the electronics required, designs have been carried out separately for the PFC, inverter and DC/DC converter. This approach is inefficient and involves significant repetition which, if eliminated, can reduce the design burden and bring chargers and vehicles to market more rapidly.

No matter the power level, almost all chargers have a common architecture encompassing a PFC stage followed by isolated DC/DC conversion and filtering. Delving deeper into the design, the topologies chosen are often the same and within these, circuit elements are often repeated.

For example PFC, dual active bridge (DAB) and LLC converters that are often used for charging contain multiple single bridge legs – a feature that is also used in motor inverters.

Leveraging this fact, Toshiba has reimagined the design process and developed the Modular EV Charger PFC Reference Design Concept – known as their ‘SiC Cube’.

This innovative design comprises seven PCBs that combine to create a very compact PFC solution. The central three boards are the bridge legs common to all mentioned circuits. They are designed in a 3-level NPC topology using SiC MOSFETs, SiC diodes and isolated gate drivers.

The remaining boards are input inductor and output capacitor boards (with current and voltage measurement), the signal connecting backplane and the control board housing an ARM® Cortex®-M4F microprocessor with advanced PWM units and the Vector Engine – a hardware engine that offers the possibility to offload the CPU during algorithm execution.

The compact dimensions of just 140 x 140 x 210mm house a design aimed at delivering 22kW of power with a 0.99 power factor and 99% efficiency at a power density of 3kW/dm³.

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