Motor voltage measurement

Hi guys, I’m working on an EV motor control project, the motor type is IPMSM, and on it’s Drive, I have found that it measures the motor voltage feedbacks (middle point of inverter legs) by Op-amps (inverting Configuration) → MCU input.

The inverter is two-level, so we have a PWM-type waveform.
The control system uses these measurements directly on its algorithm; switching got disturbed after cutting one of the op-amps inputs off. And motor stops.

My question is that what is the application of those measurements? Does anyone have a similar experience? Industrial Drives doesn’t include this section; so, I think it’s specifically for EV traction applications.

This Drive uses a single shunt current sensing method + Hall position sensor for closed loop.

The circuit schematics and output waveforms are attached.

Hey @omid96 , welcome to SimpleFOC!

Perhaps some other user have some other ideas, but perhaps it is a circuit for current measurement, using the MOSFETs RDSon as the resistance. The op-amp amplifies the differential voltage across the FET.

I’m not sure about the diodes in the drawing, though, are they being used to offset the voltage? I have to think more about it. The other option I see is that it would be used to detect the BEMF zero crossings, but I’d have to think about how the circuit is accomplishing this.

Could it be that the diodes are there to limiting the input volktrage of the opamp to app. 1.4V?

This is another reason things have to be open source. If you had the source code you could just look in there, it reduces the degree of expertise it takes to do anything, and no one can be an expert at everything.

Is it possible the motor is actually using sensorless drive using back emf commutation and the hall sensors are for something else? Or not actually being used? There are many uses for the voltage in that area in sensorless drive but it doesn’t seem to me to have much application in the case of sensored drive but I’m not an expert…