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Speed measurement and estimation algorithms in AC Induction Motors

In this paper, the multiple period speed measurement is compared with the classical frequency and/or period methods used. The proposed speed method is used to examine the quality of the three implemented speed estimators. These estimators get the information from measured stator currents and from motor stator voltage. Open loop estimators or observers are used to estimate rotor or stator flux and rotor speed to use as feedback signals. An improved open loop estimator, an MRAS, and an EKF observer are tested utilizing a 7.5 kW induction motor. They have different accuracy, robustness and sensitivity against parameter variations and all of them have the same problem when the rotor speed is around zero.