A Decoupling Estimation Scheme for Rotor Resistance and Mutual Inductance in Indirect Vector Controlled Induction Motor Drives

Coupling between the two parameter estimation loops, for rotor resistance and mutual inductance of an induction motor (IM), is presented and the resulting negative effects are discussed in this paper. To solve this problem, an online estimation scheme, estimating these two parameters in a decoupled way, is proposed for indirect vector controlled IM drives. The estimation scheme is implemented with a model reference adaptive system for the rotor flux. The reference model is taken by two sliding mode observers (SMOs) operating in series, i.e., a high-order terminal SMO, observing the defined back-electromotive force (EMF), and a first-order SMO, observing the rotor flux itself with the obtained back-EMF as its reference. Meanwhile, the current model of IM depending on both of these two parameters is chosen as the adaptive model. The error signal, driving each of the adaptive mechanisms, originates from the errors in magnitude and phase of the fluxes obtained in above two ways. The coupling between these two estimation loops are compensated by designing the weighting factors assigned to these two errors properly. Thus, the proposed scheme is decoupling, resulting in a significantly improved dynamic performance of the estimation. With the estimated parameter values, the slip speed can be calculated correctly and the field orientation can be achieved. Moreover, the torque tracking accuracy can be guaranteed. All of the analysis and design are validated through numerical simulations and laboratory experiments.