Strategies for magnetizing speed-sensorless induction machines

Whenever possible, only easily measurable quantities like stator currents a nd DC link voltage are used to control inverter-fed induction motors nowada ys. Also for high-performance AC drives speed-sensorless control of inducti on motors has received increasing attention from the viewpoint of cost, tro uble immunity and reliability. Different algorithms for speed identificatio n are known. They allow good performance of torque or speed control in almo st the whole operating area of an induction machine without using rotationa l transducers. One remaining problem is to start the machine when mechanica l speed is not known. This paper now presents two new strategies for magnet izing a demagnetized speed-sensorless induction machine also with non-zero speed.