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Part Number: DRV8711
We are using the DRV8711-EVM to drive a motor that is fairly inductive (200 step/rev, 6.5mH, 2.1 ohms). For accuracy, we need to use microstepping of 64, and for speed, we need pps =100kHz. Our power supply is 28V, though we could use a 48V supply. We set the torque register to get 1A through the motor. As we try to increase the speed, our current waveform deviates from a sinusoid and becomes triangular. We are using the forced fast decay mode. Increasing the supply from 28 to 48V helps, but doesn't quite get us to where we need to be. TBLANK = 1.5us, TOFF = 5us, ISGAIN=40.
Any insights as to how we could improve things?
Rick DuncanMotor Applications Team
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In reply to Rick Duncan:
Thanks. We are still experimenting with your suggestions - so far, it still seems like we fall short (we don't have the option of changing motors). We have observed something that we can't explain - as we increase the step frequency from what is a "good" frequency ("good" meaning that our current waveform looks undistorted), we find that we the current gets more distorted and then starts looking more reasonable again. Can you explain what's going on?
In reply to Timothy Luca:
Could you elaborate a bit more on how "the back EMF moves to a point where it new assists"? I don't understand how it can do that.
Could you explain how the back EMF can assist? I don't understand.
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