Stator resistance tuning in an adaptive direct field-orientation induction motor drive at low speeds

A novel simple stator resistance estimation technique for high-performance induction motor drives is proposed. It makes use of a synchronously revolving reference frame aligned with the stator current vector, so that the resistance can be straightforwardly derived from the mathematical model of the induction motor. A sensorless direct field orientation scheme is employed to validate the proposed solution, with the drive operating in the critical area of low speeds. A combination of two observers is used: a Kalman-filter observer to estimate the rotor flux, and a MRAS observer for speed estimation. The stator resistance estimator alleviates the usual performance degradation of MRAS-based drives at low speeds, caused by the thermal drift of that resistance. Computer simulations, including realistic disturbances, show high effectiveness of the described approach. Comparison of performance of the drive with and without the proposed stator resistance estimator demonstrates a crucial role of that device.