The active flux concept for motion-sensorless unified AC drives: A review

Rotor and stator flux orientations are now standard concepts in vector and direct torque control of ac drives. The salient-pole rotor machines, where magnetic saturation plays a key role, still pose notable problems in flux, rotor position and speed estimations for motion-sensorless control, especially in the low-speed range (below 30 rpm in general), leading to numerous dedicated state observers. This paper review introduces a rather novel (or generalization) concept - active flux or torque-producing flux - and its utilization in all ac drives by employing a unified state observer for motion-sensorless control in a wide speed range. The active-flux concept ”turns all salient-pole traveling field machines into nonsalient-pole ones”. The active-flux vector is aligned to the rotor axis for all synchronous machines and to the rotor-flux vector axis for induction machines. This way, the rotor position and speed observer seems more amenable to a wide speed range, with smaller dynamic errors. This observer, based on the active-flux concept, is pretty much the same for all ac drives. Example of implementation, for IPMSMs, RSM, dc-excited SM with experiments are reviewed to illustrate de concept.