Stabilization of the regenerating mode of full-order flux observers for sensorless induction motors

This paper deals with the full-order flux observers for speed-sensorless induction motor drives. An unstable region encountered in the regenerating mode at low speeds is well known. To remedy the problem, a modified speed-adaptation law is proposed. Instead of using only the current estimation error perpendicular to the estimated flux, the parallel component is also exploited in the regenerating mode. Using steady-state analysis, a linearized model, simulations, and experiments, it is shown that the proposed adaptation law removes the unstable region.