Estimation of the flux linkage in a direct-torque-controlled drive

An improved integration method is presented for the estimation of the stator flux linkage for speed- and position-sensorless direct-torque-controlled AC machine drives. The method is based on monitoring the scalar product of the estimated stator flux linkage and the measured stator current. The AC part of the scalar product is extracted using filtering and the correction for the estimated stator flux linkage is formed from that part. Adequate performance is obtained by using simple low-pass filtering. By using adaptive filtering in the extraction, the performance of the drive is excellent. Both simulation and laboratory test results are presented, which show that the presented method works well both in steady state and in transients.