Observer Scheme for State and Parameter Estimation in Asynchronous Motors with Application to Speed Control

The paper by Ţiclea and Besançon is an interesting contribution to the area of state and parameter estimation for both speed sensorless operation and insensitivity to parameter variation of an induction motor drive. It treats the problem of simultaneous state and parameter estimation in induction motor. It is to be noted that simultaneous estimation of speed and rotor resistance was, for a long time, considered impossible by many researchers in this area. This is because under constant flux operation in rotor flux oriented control, the rotor model is reduced to one equation containing both speed and rotor resistance. So, a change in either rotor speed or rotor resistance has an equal effect on the electrical behaviour of the motor. The aim of this discussion is to highlight the essential points about the proposed observer that can help the reader to better appreciate the significance of the paper. The authors present a method of simultaneous estimation based on an exact Kalman-like observer. The use of such an observer is made possible by an immersion of the nonlinear model of the machine into a model which is affine with respect to variables to be estimated. The choice of this observer is due to the drawbacks of the extended Kalman filter, usually used for this kind of problem [2], such as uncertain global, low accuracy at small speeds and the required computational time. The theoretical background of the machine modeling in order to use an exact Kalmanlike observer is interesting and the simulation results are satisfactory for state and parameter estimation and speed control. The method developed is weakened by the large amount of computations, when all variables of state and parameter are to be estimated as Ţiclea and Besançon have mentioned in their conclusion and it can be seen in the state vector size of the developed machine model. Also, the load torque is considered as a constant parameter which is not always the case, and this reduces the application area of the study. These disadvantages will not reduce the interest generated by this work. The machine model takes into account the coupling between the electrical and mechanical modes, and is expressed in a reference frame fixed to stator ( , ), and made under an affine representation of the form: X 1⁄4 Aðu, y, ÞXþ Bu Y 1⁄4 CX ð1Þ