IGBT instead of SiC in Model 3/Y Drive Inverters?

[Beatbuzzer]

Good day!

Recently I disassembled a flooded inverter from a model 3 front drive unit, hoping to harvest some SiC FETs for other projects.
But as I made my way down to the bare transistors, I found them labeled GK0X0 instead of GK026. And as I tested them, they behave as IGBT and not as FET (characteristic voltage drop in forward direction).
So my question, has anyone else disassembled an inverter all the way down to the transistors? I thought all inverters from 3/Y build with SiC, but maybe thats not the case?
What am I on the trail of?

best wishes to you all!

[johu]

That is very interesting. So it looks like they cut cost on the front unit knowing that it is inactive most of the time (it is only used in AWD models, right?). The async motor has slightly lower efficiency but freewheels perfectly. IGBTs are cheaper then SiC FETs as far as I know.

[Beatbuzzer]

Since creating this topic I brained a little bit about it and bought a rear drive inverter. So my latest thoughts about it I shared in the last video, which was thankfully linked in the "rear drive unit hacking" thread.
As you wrote, async front is only in AWD and in terms of efficiency and range most of the time switched off. So losses due to higher voltage drop over IGBT doesn't matter since there is no voltage
And if there is high current because of fast movement request, voltage drop over IGBT and SiC are probably nearly the same. I will prove that when I disassembling the rear inverter to harvest some SiC FETs. A little original used IGBT-FET comparison video is planned.

[Beatbuzzer]

What I can say for now is, that the gate resistors are smaller in value. For IGBT it's 4,3 ohms and for SiC it's 12 ohms because IGBT gate charge is A LOT more than SiC FET. Typical x3 for similar devices.
And gate voltages are -5V and +18V for the IGBTs. Here i think it's the same as SiC.

[Beatbuzzer]

I've made a little "schematic" to compare the gate drive stage between IGBT in front drive unit and SiC FET in rear drive unit. Left side with the transistor stage is both the same. Midpoint between the two 8V2 zeners goes to gate drive IC output. After that IGBT has 4,3 ohms gate resistance to low and high side of the driver stage. SiC FET has 12 ohms to high side, 10 ohms to low side and a diode in parallel. Seems to be a classic silicon rectifier, ultra fast type. Maybe to prevent SiC-gate from negative overshoots, larger than -5V plus forward voltage of the diode.