Sensorless Speed Control Scheme for Induction Motor Drive Using DC link Measurements

Abstract

The controlled induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, the information on the rotor speed is extracted from measured stator voltages and currents at the motor terminals. Vector controlled drives requires estimating the magnitude and spatial orientation of the fundamental magnetic flux waves in the stator or in the rotor. Open loop estimators or closed loop observers are used for this purpose. They differ with respect to accuracy, robustness and sensitivity against model parameter variations. This paper presents a new control strategy for three-phase induction motor which includes independent speed &torque control loops and the current regulation thereby overcoming the limitation (i.e. sluggish response) of volts per hertz controlled industrial drives.

For closed-loop control, the feedback signals including the rotor speed, flux and torque are not measured directly but are estimated by means of an algorithm. The inputs to this algorithm are the reconstructed waveforms of stator currents and voltages obtained from the dc link and not measured directly on stator side. The proposed drive thus requires only one sensor in the dc link to implement the close-loop speed and torque control of a three-phase induction motor.