Abstract

The permanent magnet AC motor requires absolute position information to be supplied to the controller so that the applied winding currents can be modulated in synchronism with the rotor. The design of controllers which can operate without position feedback have been the subject of intense development. The most commonly cited justifications for the elimination of the absolute position encoder are those of cost, and also reduction of the physical dimensions of the motor. The position estimation technique to be developed must be robust to external torque disturbances and preferably robust to electrical parameter variations over time. Certain military specifications apply stringent restraints to the use of sensors and estimation techniques. Absolute position encoders in this case are prohibited due to the relatively fragile nature of the glass index disk found in the encoder. The same restriction applies to manufacturers' specifications concerning electric vehicle traction drives. Fully sensorless operation has been the focus of development for all classes of electric motors, particularly the PMAC. Unfortunately, the use of state observers is viewed by industry with suspicion in terms of the computational effort required and also the question of robustness. A solution is presented which satisfies the constraints of physical and computational robustness, and is experimentally verified.