General motor control

[nForce]

When controlling some motor (DC, AM, SM) if the rotor is spinning in the negative direction and we apply positive torque. Will then the rotor slow down and start spinning in a positive direction?

And now if we have a positive torque, and the controller gets the reference value of negative speed. So now the torque goes from positive torque to negative?

Thanks.

[Sal Ammoniac]

When controlling some motor (DC, AM, SM) if the rotor is spinning in the negative direction and we apply positive torque. Will then the rotor slow down and start spinning in a positive direction?

It depends on how much torque you apply. If you apply too little torque, the rotor will slow down, but continue rotating in the original direction. If you apply enough torque, you can reverse the direction of the rotor. You can also apply just enough torque to stop the rotor entirely. These statements assume, of course, that you're applying this external torque via the motor's shaft and the motor's speed is not being actively controlled. If that were the case, the controller will attempt to maintain the motor's speed and direction (within limits, of course).

And now if we have a positive torque, and the controller gets the reference value of negative speed. So now the torque goes from positive torque to negative?

I don't know what you're asking here... If I'm interpreting you correctly, if the motor rotor is spinning in one direction, say, clockwise, and you tell the controller to set a negative (relative to the current direction of spin) speed, then yes, the motor will slow to a stop and start spinning in the opposite direction (assuming the load allows it to do so).