Cambridge GaN Devices has patented a technique for lowering losses in 100kW+ IGBT-based vehicle traction drives, at lower cost than all-silicon-carbide inverters, it said.

CGD Combo ICeGaN GaN IGBT traction inverter
It involves connecting GaN hemts in parallel with large silicon IGBTs, and has been branded ‘Combo ICeGaN ‘.

“Today, inverters for EV powertrains either use IGBTs which are low cost but inefficient at light load conditions, or SiC devices which are very efficient but also expensive,” said CGD founder and CEO Giorgia Longobardi. “Our Combo ICeGaN will revolutionise the EV industry by intelligently combining the benefits of GaN and silicon technologies, keeping cost low and maintaining the highest levels of efficiency. We are already working with tier-one automotive EV manufacturers and their supply chain partners to bring this technology to the market.”

The company’s GaN hemts are ICs that include gate drive circuits that allow them to be controlled by drivers intended for silicon mosfets up to 20V. Some also include current sensing.

The paralleled silicon IGBT and GaN hemt efficiency argument goes like this:

The GaN transistor has low conduction and low switching losses at low traction loads, while IGBTs have lower losses towards full load and during surges.

At higher temperatures, the bipolar component of the IGBT will start to conduct at lower on-state voltages, which supplements loss of current through the GaN device. Conversely, the Gan devie takes more current at lower temperatures.

The avalanche clamping capability of IGBTs protects the GaN hemts from voltage surges.

Sensing and protection functions, along with optimal driving, can enhance the safe operating area of the combined hemt+IGBT.

Why not parallel a silicon mosfet with the IGBT?

“High voltage silicon mosfets are not good choice for traction inverter application due to its high body diode reverse recovery loss, so silicon IGBTs or SiC mosfets are commonly used in traction inverters.” CGD told Electronics Weekly.

What efficiency gain will paralleled GaN transistors offer?

“Compared to a silicon IGBT solution, Combo ICeGaN with 30% GaN and 70% IGBT for a standard 150kW 800A power module can have >40% lower average energy loss per WLTC driving cycle,” it said. “At light load, 100-200Arms, where the inverter operates most of the time, the inverter loss can be reduced by more than 1.5x versus silicon IGBTs. This translates to 3-4% longer EV range or battery pack cost saving due to the energy saving on the inverter.”

And compared with an all-SiC inverter?

“While a full SiC module offers better performance, Combo ICeGaN die cost is estimated to be 35-40% lower than full SiC module, so it offers good combination of system cost and performance,” said CGD.

The company holds a patent on this technology and will be exhibiting at APEC (Applied Power Electronics Conference and Exposition in Atlanta (stand 2039, 16-20 March).
Technical details were first revealed in a paper at the IEDM conference in December 2024.