Setting motor parameters: Rs, Ld and Ld/Lq ratio

[jouko.perkkio]

I have 5kW QS138 BLDC motor within my e-bike project with my own motor controller electronics. I have measured inductance and series resistance from the motor with a precision LCR meter:

	Lq [mH]	Rs [ohm]	Ld [mH]	Rs [ohm]		Ld/Lq
120 Hz	0.031	0.003	0.021	0.003		0.67
1 kHz	0.030	0.111	0.021	0.067		0.69
10 kHz	0.027	0.210	0.019	0.148		0.72
20 kHz	0.025	0.575	0.018	0.390		0.72

At MCSDK one inserts the motor parameters and other drive settings. My PWM frequency is 15 kHz with equal FOC update rate. Now should the motor parameters be inserted to the program as measured with this PWM frequency? Or are they assumed to be "static DC values"?

By using "15 kHz" values, I get following parameters: Rs = 0.2 ohm, Ld = 0.019 and Ld/Lq = 0.72

Going to the "DC end": Rs = 0.003 ohm, Ld = 0.021 and Ld/Lq = 0.67

Any suggestion which is the correct end to start iterating? 

[Gael A]

Hello joukio.perkio,

You should go for the DC values. It does not really matter for the inductance, as it stays fairly similar (as it should), but the resistance changes a lot depending on frequency. You can also use the Profiler feature from the MCSDK that allows you to retrieve all the required motor parameters.
You can enable the feature via WB in the Application Configuration tab, and find guides on how it is working on our MC wiki and User Manual (and HSO start-up guide if you are using this observer)

[jouko.perkkio]

Thank you! Definitely looks like that the DC values are the way to go.

Initially I tried to use the motor profiler. It was not able to finish the profiling, regardless of the current or RPM limiting settings I had tried. I suspect that the profiler has problems with such a low-inductance motors. It did get it spinning, but with awful squeeking noise, consuming enermous amount of current and eventually failed to finish the profiling.