Design method of a simplified speed observer for speed sensorless F.O. induction motor drives working at low speed in 4-quadrant mode

In this paper, a design method for a simplified speed observer for a speed sensorless field oriented (F.O.) controlled induction motor drive is proposed. The method is based on the stability analysis of the drive operation, on the torque vs. speed plane. A decoupling control is used to generate the voltage commands from the current commands instead of current regulators. The speed is estimated using a Luenberger speed observer, whose structure is simplified taking into account the decoupling control equations. Special attention is given to the stability of the drive operation at low speed both in motoring and in regenerating operation. The validity of the proposed method is shown by simulation results.