Improved Stator Flux Estimator for Speed Sensorless Induction Motor Drives

In this paper, an improved induction motor (IM) stator flux estimation method is proposed, based on a novel integrator scheme with a closed-loop dc offset compensation algorithm. When compared with the existing stator flux estimators, the proposed solution represents an improved programmable low-pass filter. Namely, by introducing a novel closed-loop dc offset compensation structure, two major drawbacks of existing stator flux estimators are overcome; their stability and accuracy at low frequencies, and the estimator response time over the whole frequency range, introducing an estimation algorithm much simpler than existing solutions. The performance of the novel stator flux estimator is tested by means of simulation runs and experimental tests, with the proposed algorithm used for the estimation of the stator flux, rotor flux, and rotor speed in a direct field-oriented controlled IM control algorithm. The simulations and experimental results show that the proposed estimator enables accurate and stable operation under all operating conditions, including the critical low stator frequency range.