A novel adaptive vector control system for temperature compensation in induction motors

Abstract

A new method for the improvement of temperature variation in the Induction Motor (IM) s p e d control is presented in this paper. A direct measurement of the rotor temperature is assumed. The compensation of the temperature effect is made not only by adjusting a digital filter flux model coefficients but also by calculating the on-line Proportional Integral (PI) controller coefficients. These corrections yield matching of the flux model and the induction motor model, consequently the magnitude of the reference rotation and the induction motor model angle's are equal so the matching of the command estimated variables and the real variables of the induction motor is obtained. This method uses the direct field-oriented vector control and eliminates its main disadvantage which is the decoupling of flux and torque when a rotor time .constant varies. The simulations have shown an improvement mainly in the transient state response. k*(t) = Conjugated complex current vector.Once the flux density on the stator si& of the air gap is calculated. the flux linkage can be obtained for each stator winding and the combination of the three scalar flux linkages gives the instantaneous stator flux wave which is:where;Similarly the rotor flux is :The ficld oriented control method allows an excellent motor dynamic performance. The knowledge of the rotor flux position detcrmincs whether the vector control scheme is direct [5], [7] (flux measured) or indirect [9], [12] (Bux estimated). The indirect vector control is more popular due to the absence of field angle sensors and the ease of operation at low speeds [9]. However it is very sensible to parameter variations due to temperature changes [lo], [12].The machine parameters dependency was discussed in many papers (31.[ l l ] . whcre the proposed solution was based on parameter adaptation. Unfortunately many of these methods are not easy to iinplcmcnt and the speed of response is to be evaluated.To overcome this disadvantage a simple and reliable method is presented here. It is assumed that rotor's temperature measurement is obtained in real time. The proposed method uses the direct vector control scheme [12], where the most important parameter to v i e care of is the rotor time constant variation (ATR). This paper begins by reviewing the mathematical model of the induction motor and the vector control equations. Then temperature vnrintion correction is dcvcloppcd by adapting the flux model on one hand and the controller's constants on the other hand. Finally simulation results and conclusion comments are presented. MATHEMATICAL MODEL OF THE INDUCTION MOTORThe niatlicmatical equation of the familiar three-phase induction motor are remainded here [2]. [6] . We have used the AC machine niodcl and its control in field co-ordinates, assuming impressed stator cuncnts and current control in stator co-ordinates [8]. The mathcmatical approach given by W. Leonard [ 11 is used here, where a symmetrical three phase windings having sinusoidal spatial magneto motrise force (m.m.f.) distribution is ...