Improved rotor flux estimation based on voltage model for sensorless field-oriented controlled induction motor drives

Speed sensorless field-oriented vector control of induction motor depends on effective estimation of rotor flux. This paper proposes an improved rotor flux estimator based on stator voltage model with programmable low-pass filter (LPF) and an error compensator. In the voltage model based flux estimation, a LPF is normally used to replace the pure integrator to avoid integration drift and saturation problems. However, the LPF estimator may introduce magnitude and phase errors, and results in degraded estimation performance at low operating frequency. The flux estimation error is compensated according to feedback signal of the estimated flux in this paper. In addition, the LPF with a fixed cutoff frequency is difficult to provide good estimation for wide speed range. The reason is that lower cutoff frequency required for wide speed operation may result in weakening the restraint of dc drift problem. To achieve the compromise, an improved programmable LPF rotor flux estimator with a compensator for dc drift restraint is introduced. The validity of the proposed rotor flux estimator is verified by speed sensorless field-oriented vector controlled 11kW induction motor. Experimental results demonstrate high performance of the improved rotor flux estimator.