A Comparative Study of Flux Observers in Induction Motors

Abstract

In this paper, a comparison of three rotor flux estimation techniques for the three-phase induction motor is presented. Three types of observers are suggested to be compared for flux estimation, open-loop flux observer, nonlinear flux observer, and sliding mode flux observer. These observers are compared according to their, simplicity of design, implementation, and convergence rate of estimated flux to the actual value. The three-phase induction motor model is derived according to the basis of nonlinear control tools. The reference frame theory is assessed and the importance of the relationship among these reference frames is clarified in accordance with the estimated flux. The three observers are designed and the stability analysis is assessed according to the Lyapunov stability analysis. Matlab has been used to simulate the three-phase induction motor in an open loop configuration with the three observers. Sliding mode flux observer was faster than the two others observers, open-loop flux observer was the simplest one with the less robust characteristics, nonlinear flux observer showed controllable convergence rate with simple observer structure. Theoretical hypothesises are confirmed through the observations simulation results comparisons in the stationary and synchronous reference frames. Index Terms— Induction motor, Flux observer, Field orientation, Sliding mode observer.