Sensorless vector control scheme for induction motors based on a stator flux estimator with quadrant error compensation rule

Accuracy of flux information is critical to the performance of sensorless field-oriented control. The stator flux is simply estimated by integrating v_s-R_si_s. However, this integration method deteriorates easily in the low-frequency region due to a DC offset, voltage error caused by dead time, stator resistance error, etc. Thus, sensorless field-oriented control methods mostly yield poor performance around zero speed and zero frequency. In this paper, a new flux error compensation rule, namely, the quadrant error compensation rule is proposed. The polarities of compensating terms differ depending on q-axis current (torque) and angular frequency of the flux. Specifically, the polarity and magnitude of the compensation terms are chosen differently depending upon rotational direction and whether the motor is in the motoring mode or in the regenerating mode. The compensating terms are calculated based on error between the measured current and the auxiliary current estimate which are obtained by filtering the estimated flux. Simulation and experimental results show that the proposed scheme yields improved performance in both zero-speed and zero-frequency operation under the rated load, even when there is significant stator resistance error.