Rotor shaft angle estimation

Bert,

The rotor flux angle is related to the rotor angle.  It is the net vector oriented in the north pole direction of the magnetic field of the rotor.

FAST needs Bemf feedback from the rotor, which you only get by having the rotor move, so it is only appropriate to replace encoders in applications where the rotor is moving, i.e. velocity+torque applications.  How slow you can go depends on the Bemf of the motor (bigger is better) and the resolution of the voltage signals.  < 1 Hz is typical.  And you can pause at zero as a transition.  You can also hold at 0 speed, sometimes for a very long time, but FAST can't guarantee a change in position due to a transient event...but you can have a transient event and then have 0 speed control once it recovers (again, depending on Bemf and sensing).  We have actually run in the mHz range with decoupled high resolution sensing into the agorithm.

If position control is required today you need a mechanical sensor, typically encoder or resolver for the resolution required.

However, there are rotor angle observer algorithms that don't rely on Bemf, and they can work at very, very low speeds, 0 speed, and potentially zero position.  These are things we are investigating, but for now the answer is "position control requires a mechanical sensor).