Strategies for magnetizing speed-sensorless induction machines

Whenever possible, only easily measurable quantities like stator currents and DC link voltage are used to control inverter-fed induction motors nowadays. Also for high-performance AC drives speed-sensorless control of induction motors has received increasing attention from the viewpoint of cost, trouble immunity and reliability. Different algorithms for speed identification are known. They allow good performance of torque or speed control in almost the whole operating area of an induction machine without using rotational transducers. One remaining problem is to start the machine when mechanical speed is not known. This paper now presents two new strategies for magnetizing a demagnetized speed-sensorless induction machine also with non-zero speed.