GaN in an EV inverter? Here is a prototype

Is gallium nitride (GaN) ready for EV inverters? That was the crux of an APEC 2023 keynote titled “GaN for EV Power Train: Breakthroughs and Challenges.” During her keynote, Tamara Baksht, CEO and co-founder of VisIC, provided the technical details of a three-phase GaN-based inverter reference design developed with 400 V bus voltage and 400 A RMS current.

The reference design drives 4 GaN dies in parallel to obtain equal current sharing and smooth waveform, leading to low voltage overshoots on the gate and drain. Parasitic signals and spikes are controlled by the Miller clamp. Next, while GaN doesn’t have a body diode, reverse conductivity is carried out through the same channel. That may lead to oscillations, calling for tuning with external capacitors.

In an inverter design, made for peak load conditions, switching losses dictate efficiency. Baksht mentioned Tesla S Model, which accomplished 4% efficiency and 10% boost in driving range when it made switch from silicon to silicon carbide (SiC) semiconductors in 2018. Here, she was quick to note that GaN offers a significant cost advantage compared to SiC. “But the main challenge is inductive load switching.”

Source: VisIC

Regarding the 400 V inverter reference design paralleling multiple GaN devices, Baksht acknowledged that it’s just the beginning. “It should be improved, and it will be improved.” Nevertheless, the reference design demonstrates that it’s possible to power EV inverters with GaN semiconductors.

However, she acknowledged that while GaN can operate in a 400-V car successfully, there is a lot of work ahead of us before we bring GaN in real cars on real roads. “Cooling and thermal management are huge challenges for GaN devices in EV powertrains.” Baksht also mentioned circuit protections that should be fast enough and cooling that is synchronous as major issues.

According to Baksht, the inverter solution alongside a motor has been tested at an OEM customer site. And it has been tested with up to 113 kW ratings. She concluded by saying that while GaN-based inverter prototypes are here today, seeing GaN devices serving EV inverters at mass production may take five to six years.

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