Model-based speed identification for induction Machines in the whole operating range

A speed observer for induction machines without rotational transducers is presented. In contrast to known adaptive observer strategies, the proposed scheme uses-beside the conventional current difference-its integral and a new pair of stretch-turn operators not only to avoid the known instability region at braking but to obtain furthermore a constant gain. To ensure operation with very low stator frequencies, an elimination of parasitic dc components is presented additionally. Characteristics are explained and verified by measurements.