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Unread 05-05-2009, 19:21
vamfun vamfun is offline
Mentor :Contol System Engineer
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Re: Sensorless back_emf speed controller

Got a preliminary look at the JAG waveform:
PWM generated with VEX controller
9 volt power supply (all I had)
CIM-01 no load

Looks like the inductive spike settles in 15 to 20 % of the wave form period. This is what I would call a 3*L/R period.... so I'm guessing the L/R is in the neighborhood of 1/15kc * (.15/3)= 1/300 ms . My motor leads are short so with some added wire resistance this might conservatively decrease to about 1/500 ms or about 2 us.

So it seems that the inductive spike settling is not the driver for the motor shut down to measure the back_emf. One could just shut it down for a pwm cycle, make the reading and turn the controller back on. The controller restart might take a cycle or two to get going but that wouldn't be too bad.

I ran the waveform with braking and coast mode. It was strange that the coast mode waveform didn't appear any different. This is not what I expected...so maybe someone can verify this.

Last edited by vamfun : 05-05-2009 at 20:26.