Sensorless induction motor control with improved stator flux estimator by programmable LPF

In this paper, the improved stator flux estimator has been proposed to ensure A Programmable Low Pass Filter (PLPF) to act as a pure integrator for sensorless control of induction motors. Conventional PLPF uses the estimated synchronous speed as a cut-off frequency, with the magnitude and phase compensator determined on the assumption of the estimated synchronous speed being coincident with the actual one. However, if the synchronous speed is not exactly estimated, the magnitude and phase compensation will not be appropriate. Therefore, this paper has analyzed the relation between the synchronous speed error and the phase lag error of the stator flux. Based on this analysis, the synchronous speed error compensation scheme is proposed. In addition, this paper proposes the flux error compensation scheme because there still remain errors in spite of the speed error compensation. The validity of the proposed estimator has been proven using the simulation results.