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DRM077 and MC56F8037 using vector control for low speed hub ebike motor

Question asked by Tim Economu on Nov 21, 2008
Latest reply on Dec 31, 2008 by Tim Economu
I would like to use a reference design for a brushless ebike hub motor. I also want to use the sensorless PMSM software to allow the use of field oriented control (FOC) and space vector modulation (SVM).

DRM077 supports both the use of BLDC (trapezoidal) and PMSM (sinusoidal) sensorless drive methods, so that is good. Only problem I can see: the specifications for the reference design, on page 23 are the words "Motor control has a speed range of 300rpm to 4500rpm."

The hub motor has a speed range of about 15 RPM (slow pedalling) to a MAX speed of 300 RPM, and in looking at the code in Codewarrior, and checking DRM077 it is not clear what happens at low rpm. There does seem to be a sofstart variable, but I am not clear if the low rpm uses the FOC and SVM methods, or is there just a canned lookup table for slow speed start.

So my questions are: Does the slow speed startup of DRM077 use FOC and SVM, and if so great. If not is there a way to make them do that, or is there another solution that will work at low RPM? Is there another sensorless solution? I know the QE128 now has a new reference design but that uses an encoder that is many times the cost of a micro, so that is not a solution.