Sensorless Sliding-Mode Rotor Speed Observer of Induction Machines Based on Magnetizing Current Estimation

This paper presents a rotor speed observer for induction-machine drives based on a sliding-mode approach and magnetizing current estimation. The back electromotive force (EMF) is calculated from the stator current and the stator voltage signals. The magnetizing currents are obtained from the back EMF. A theorem which gives the rotor speed estimate in the continuous-time domain is formulated using the magnetizing current estimation. The stability analysis is achieved based on the Lyapunov approach. Moreover, the discrete-time approach of the method is discussed, and a theorem for the discrete-time implementation is proposed. The limits that ensure the system stability for the switching gains and for the observer gain are discussed. This paper shows that the limits for the gains of the discrete-time algorithm are different from the limits for the gains of the continuous-time algorithm. Simulation results are presented to validate the theoretical analysis. In addition, experimental results based on a fixed-point digital signal processor (DSP) platform (DSP TMS320F2812) demonstrate the performance of the proposed scheme.