A new graphic method for stability analysis of speed sensorless FO controlled induction motor drives working at low speed in regenerative mode

In this paper, a graphic method to analyze, on the torque versus speed plane, the stability of a speed sensorless field oriented (FO) controlled induction motor drive is proposed. A decoupling control is used to generate the voltage commands from the current commands instead of the traditional current regulators. The speed is estimated using a Luenberger speed observer, that has been simplified taking into account the decoupling control equations. Special attention is given to the stability of the drive operation at low speed, in regenerative mode. This makes the proposed method interesting when the sensorless drive control has to be designed, for example, for electric vehicles applications. The proposed method has been simulated and the results obtained are shown in this paper.