SENSORLESS POSITION DETECTION FOR VECTOR-CONTROLLED INDUCTION-MOTOR DRIVES USING AN ASYMMETRIC OUTER-SECTION CAGE

This paper describes a new method of obtaining a rotor position signal from a cage induction machine operating without a mechanical sensor. The method is based on introducing a circumferential variation in the resistance of a high-resistance outer-section cage of an induction-mac hine rotor, Simulation results using a linear ''double-cage'' machine equivalent show that the method is feasible and provides incremental r otor position tracking with good dynamics, The paper describes an impl ementation of the method for a 30-kW double-cage machine having variab le-gauge copper wire in the outer slots, It is shown that, while the r otor position-dependent signals are robust to changes in load, interfe rence harmonics arising from slot saturation and rotor slot harmonics cause problems for rotor position tracking, These problems are discuss ed in relation to the present method and that of designed asymmetries in general.