A sliding mode observer for sensorless induction motor speed regulation

A novel sliding mode observer for current-based sensorless speed control of induction motors is presented in this article. The control objective is to guarantee asymptotic tracking of prespecified references for speed and rotor flux magnitude, without sensors measuring the mechanical speed and the flux, and assuming to have some kind of uncertainties on the value of the rotor resistance. To this end, the proposed observer is designed by coupling a second-order sliding mode observer of the stator current with a nonlinear flux and speed observer, adaptive with respect to the rotor resistance. Estimation of unknown inputs is based on a different and original approach with respect to the widely used equivalent control-based techniques. As for the control aspects, in the present proposal, the problem of chattering, typical of sliding mode controllers, is made less critical since the derivative of the stator currents are used as discontinuous forcing actions, while the actual control signals are continuous, thus limiting the mechanical stress.