finding the cause for MOSFET burning STM32G431
Hey @ all
the setup:
- custom motor control PCB
- microcontroller: STM32G431CBU6
- gate-driver: UCC2721, 15V
- three shunt lowside current sense 150 µOhm
- OPAMP MAXIM MAX40056 20V/V
- inverter stage: 24x IRF7759 (4 parallel)
- gate resistor 4,7 Ohm
- gate-source resistor 20 kOhm each FET
- motor: 48V, 3 PP, Rs = 4mOhm, Ls= 10 µH, BEMF 3,3 Vrms/kRPM, 200A DC max, 10.000 RPM max
Workbench settings:
The motor runs fine even at 8000 RPM. The problem is that under small load of 2 kW (48V, 50 A DC, 4000 RPM), after 1-2 minutes of constant speed, a MOSFET burns through with an explosion, although the temperature at the inverter stage is only around 40°C and the FETs are cooled through a thermopad (1mm thick, 12 W/mK) and pressed onto a water cooled aluminium body. The cooling should be more than sufficient, as the same cooling system works fine on a motor controller from the competition with the same motor under full load (12 kW, 200 A DC) for 10 minutes and FET temperature <80°C.
I am trying to find the cause for the MOSFET burning. Could it be caused by bad current and flux PI regulator settings? The settings I use are automatically calculated parameters from the workbench, I didnt tune them myself and they can be seen in the screenshot above. The motor runs smooth though. I can provide a current reading of one of the OPAMP outsputs from the current measurement during operation (pink color):
INFO: the huge voltage spikes during switching are caused by long measurement wires and are not "real".
Could any other wrongly-set parameter cause excessive heating or switching losses of the FETs that could lead to mosfet burning ?
Any suggestions are appreciated.