A novel adaptive observer for very fast estimation of stator resistance in sensorless induction motor drives

The performance of sensorless vector-controlled induction motor drives is generally poor at very low speeds due to offset and drift components in the acquired feedback signals, and the increased sensitivity to model parameter mismatch. The stator resistance variations resulting from temperature and frequency changes, produces deviations in the flux, and as a result the speed estimates particularly at very low speeds are greatly affected. Therefore a compensation scheme for the parameter variations is vital, especially in very low speed applications of sensorless induction motor drives. This paper presents a novel method of estimating the stator resistance of an induction motor, based on adaptive control theory. In this novel scheme, an adaptive pseudoreduced-order flux observer (APFO) is used instead of the adaptive full-order flux observer (AFFO). In comparison with the AFFO, this method consumes less computational time, and provides a better performance at very low speeds. Both simulation and experimental results of the proposed stator resistance scheme have shown that the proposed method is faster than those based on AFFO, and further the simulation results have demonstrated satisfactory performance over an entire range of resistance variations from 0 to 100%.