[MPaulHolmes]

Thanks for the suggestions Automcdonough!

dcb, I think that's it. The torque and flux components are at right angles. If the flux vector you are commanding isn't aligned with the rotor flux vector, I guess it's just a waste of power. I think in that situation, the torque component isn't happening at exactly a right angle, and it's a waste of torque. Like trying to turn a wheel by pushing straight in toward the axle rather than tangent to the wheel.

The real reason I ordered the fine resolution speed sensor was because the application note said I needed rotor velocity to compute rotor flux angle. I didn't really have a clue what any of that meant, so I just ordered it. haha. You can do sensorless, but it's harder. Heck, even AC FOC seems like it won't be easy. Everything about finding the motor characteristics to optimize the FOC equations seems proprietary. No company wants to explain how they do it.

I think it would work fine with a brushless DC. Actually, brushless DC would be easier, since the rotor angle and rotor flux angle would be the same, because of the permanent magnets. And the rotor flux angle is the horror to compute. Also, in that case I_flux is just set to 0, since you get the rotor field for free. All you need to worry about is I_torque. Then for field weakening, you actually set I_flux negative, and it fights against the magnets of the rotor, making them weaker, allowing higher rpm.