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MPaulHolmes · 09-15-2015, 06:01 PM

I think I may have found a way around the noise issue TI was talking about with one of the major steps for doing sensorless FOC:

Ea = Va - R * I - L * dI/dt

The trouble is, you have to compute dI/dt, but the current waveform is noisy in general. I found the graphs of some of I(t) by printing out the data while the motor was running, and gosh darn it, even down to zero RPM, they are sine waves, but jaggedy due to the noise! So, just figure out the period and magnitude, which are more noise immune (when does it cross x-axis, when does it reach a peak) and then don't do a numerical derivative (i - iOld) / 0.0001), but instead do cos(theta) = d(sin(theta)/dtheta so then your derivative is not noisy!

09-15-2015, 06:01 PM	#2007 (permalink)
MPaulHolmes PaulH Join Date: Feb 2008 Location: Maricopa, AZ (sort of. Actually outside of town) Posts: 3,832 Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000 Thanks: 1,362 Thanked 1,202 Times in 765 Posts	I think I may have found a way around the noise issue TI was talking about with one of the major steps for doing sensorless FOC: Ea = Va - R * I - L * dI/dt The trouble is, you have to compute dI/dt, but the current waveform is noisy in general. I found the graphs of some of I(t) by printing out the data while the motor was running, and gosh darn it, even down to zero RPM, they are sine waves, but jaggedy due to the noise! So, just figure out the period and magnitude, which are more noise immune (when does it cross x-axis, when does it reach a peak) and then don't do a numerical derivative (i - iOld) / 0.0001), but instead do cos(theta) = d(sin(theta)/dtheta so then your derivative is not noisy! __________________ kits and boards Last edited by MPaulHolmes; 09-15-2015 at 06:15 PM..