Decoupled Stator Resistance Estimation for Speed-Sensorless Induction Motor Drives Considering Speed and Load Torque Variations

There are many adaptive full-order observer (AFO)-based simultaneous speed and stator resistance estimation techniques for speed-sensorless induction motor (IM) drives. However, they still need to be improved since the stator resistance estimator is sensitive to speed and load torque variations, especially under low-speed and light-load conditions. In response to this problem, an improved 'phase-shift'-based compensation method is proposed for the stator resistance estimation in this paper. Compared with the existing methods, the proposed stator resistance estimation approach is decoupled with the speed estimator by adopting an operating-point-Tracking compensation coefficient. Accordingly, the robustness of the stator resistance estimation is guaranteed to speed and load torque variations. The neglected estimated rotor flux error is first introduced for the proposed stator resistance estimator to distinguish the stator resistance error component. Then the sensitivity analysis of the proposed compensation coefficient against parameters variations is carried out. Furthermore, the stability of the speed estimator and the stator resistance estimator is guaranteed owing to the proposed method. The experimental results highlight the effectiveness of the proposed method for improving the accuracy and the stability of the stator resistance estimator under different speeds and load torque conditions.