We're running a BLDC motor in torque-control mode, using Lab 04a on a DRV_8301 EVM kit with a 28069 Control Card. We ask for a particular amount of Q-axis current and then vary the load. The system speed reacts to the load. When we decrease the load enough to approach rated speed on our motor, the torque starts to decrease. We see a corresponding decrease in the phase current as well (as expected). We're using our own measured motor parameters in User.h. When we calculate the current phase angle from the measured phase voltage and current (on an oscilloscope), we find that the regulator does a good job applying 100% q-axis current up to a certain point, but then it seems we start to see a fair amount of field-weakening. This is strange because the commanded d-axis current is zero.
Our thought was that we needed to mess around with the current regulator gains, so I opened up Lab 5a and played around with the two gains used in the lab, but I didn't see much change in behavior. I ran the motor at 14A and 1300rpm (where we're normally starting to fall apart) and went up and down by a factor of 10 on both the proportional and integral gains, but the phase angle didn't change much. The audible noise coming from the system did change a little, and the current waveshape did change very slightly, but no improvement in torque.
Based on the motor model and our DC bus, we should be able to apply 14A (and get the corresponding torque) up through about 2000rpm. It seems like we're being limited somewhere, but the limits set up in User.h should be well above our operating point. Plus, the d-axis current injection is very odd. I'm not sure exactly where to turn at this stage, but any help would be appreciated.
Thanks,
Matt