Hi,
I am testing my PMSM motor and wanted to find the back emf constant.
In my setup, I have my motor connected to a similar motor through a shaft (which acts as a generator).
Here's the setup:
1. I ran the motor at a constant speed at 3400 RPM with a controller.
2. Back emf voltage peak is 61V on the generator (not loaded).
3. My battery voltage at that point was 57.5V.
4. And the controller has not entered into flux weakening yet. (as I see Reference Id is still 0).
My doubt:
I used to think that the motor goes into flux weakening zone when the back emf voltage gets close to the battery voltage. But in the above case, I can see that the controller has not gone into flux weakening even when back emf peak is 61V. I do not know what can be a reason for this or is there a problem in my understanding.
Some of the reasons that I can think of:
1. The ref id is 0 but the actual id has noise and keeps fluctuating around 0. That could be an error in current sense, or the effect of harmonics. But this should not be back emf much I think.
2. There is an error in the voltage measurement by the controller.
3. The flux weakening algorithm is not proper.
4. My theory is wrong. ( coz flux weakening works on Ud and Uq which correspond to the fundamental voltage of the PWM output).
5. Any other reason?
Note: the phase current waveform is very bad when measured with a current probe.
