An adaptive speed estimator for single-phase induction motors

In this paper, a mechanical speed estimator based on the model reference adaptive-system (MRAS) principle is evaluated for a single-phase induction motor operated as two-phase motor. In three-phase drives with complete vector control/MRAS system the effect of the rotor time constant is auto-compensated by the decoupling compensators or slip calculation. However, it is not feasible in pure MRAS scheme application. Further, the asymmetrical main and auxiliary windings of single-phase motors increase the estimator sensitivity to parameter mismatch and environment change. The MRAS is evaluated when the error vector choice relies on observing the counter electromotive force vector, instead of flux based MRAS structures. Also, it is analytically shown that instantaneous reactive power principle does not suppress the stator resistance in MRAS speed estimation of single-phase motor. The MRAS observer was tested under offset, no load operation and field- weakening region conditions. The MRAS performance was successful even to sharply frequency-step transitions.