Synchronization at startup and stable rotation reversal of sensorless nonsalient PMSM drives

Low-Speed Sensorless Control With Reduced Copper Losses for Saturated PMSynRel Machines

“…However, at higher speeds, where back-EMF based sensorless algorithms can be utilized, the vanishing saliency does not pose any limitation and the unfeasible region could potentially be exploited when the rotor speed decreases. Another way of entering the unfeasible region can be to initiate sensorless operation from zero speed using sensorless algorithms not relying on signal injection but which can still handle an initial startup procedure, e.g., [28], [29]. 1) Optimization Procedure: Finding optimized operating points in the unfeasible region can be determined by relaxing…”

A Combined Position and Stator-Resistance Observer for Salient PMSM Drives: Design and Stability Analysis

“…To facilitate this transition at as low a speed as possible, it is vital to use a back-EMF-based method by which an asymptotically stable system is obtained for all speeds but standstill. 1 The stator resistance is the by far most sensitive parameter at low speeds; an inaccurate model stator resistance will often result in a large position error [10], [11], [12], and possibly even instability. Among the many publications on back-EMF-based methods for PMSMs [8], [10]- [30], only a few have proposed circumvention of this problem.…”

“…1 Because the back EMF vanishes at zero rotor speed, a back-EMF-based estimator by necessity becomes "blind," and as a consequence marginally stable, at standstill. and stator-resistance observer-whereas [11] proposes usage of the instantaneous reactive power.…”

A reduced-order position observer with stator-resistance adaptation for PMSM drives

“…Since the back electromotive force (EMF) is proportional to the rotational speed of the motor, parameter errors have a relatively high effect on the accuracy of the estimated back EMF at low speeds [4]. Improper observer gain selections may cause unstable operation of the drive even if the parameters are accurately known [3], [5].…”