Speed sensorless stator-flux-oriented control of IM drive with stator resistance compensation

For speed sensorless stator-flux-oriented control (SFOC), the accuracy of the estimated flux position decides the performance of the speed sensorless drive. In this paper, a novel flux estimation method is proposed in which the pure integrator is replaced by a low pass filter (LPF) to resolve the DC-drift and saturation problem and the phase error with the LPF is approximately compensated by the reference flux component to obtain the stable low-speed operation. However, the flux error due to the stator resistance deviation still remains, especially at very low speed. Therefore, a compensating method for stator resistance variation is also incorporated in the flux estimation such that the flux estimation can be independent of the stator resistance. The method is based on a current error between an estimated current obtained by the estimated flux and the real current. Comprehensive analysis was performed to investigate the relationships among flux magnitude error, flux angle error, and current estimation error in the motoring and regenerating modes. Finally, the sensorless SFOC scheme based on the proposed flux estimating method had been implemented on a 2.2 kW induction motor. All experimental results show that the proposed scheme has improved low speed performance, even when there is significant stator resistance error.