An observer based on-line rotor speed estimation technique for a vector controlled induction machine

A novel rotor speed estimation method using model reference adaptive control (MRAC) is proposed to improve the performance of a sensor less vector controller. In MRAC methods, state variables, such as rotor flux and stator back EMF are estimated in a reference model and then compared with state variables estimated by using an adjustable model. The difference of these state variables is then used in an estimation of rotor speed. A new MRAC method is proposed in this paper that uses the stator current as the state variable for estimating the speed. In the proposed method, the stator current error is represented as a function of the first degree for the error value in the speed estimation. The proposed flux observer is designed without any integrator and is based on algebraic equations involving the measured and filtered signals. Thus, the proposed method offers a considerable improvement in the performance of a sensor less vector controller at a low speed. The superiority of the proposed method is verified by simulation and experiments.