An estimating method of instantaneous load torque by wavelet transform for the induction motor drive

In a sensorless vector control system, speed estimation in the lower speed region is difficult because of various factors. For example, torque ripple has a harmful effect on speed estimation in the lower speed region. We propose an accurate speed controller for a speed sensorless vector control system in the lower speed region. The ripple of the estimated speed is extract from the estimated speed with the wavelet transform, and the ripple of torque is estimated with the disturbance observer. To compensate the ripple of torque, the estimated ripple of torque is added to the speed controller as the torque ripple current. Consequently, the sensorless vector controlled induction motor can be driven accurately in lower speed region.