A sensorless speed estimator for the direct torque control of an interior permanent magnet synchronous motor drive

This paper proposes a completely sensorless interior permanent magnet (IPM) synchronous motor drive with direct torque control, which uses a new speed estimator from the stator flux linkage vector and the torque angle. It is shown that by including the torque angle in the estimation process results in a more accurate transient speed estimator than what is reported in the existing literature. Also, the effect of current measurement error (offset error and scaling error) are analyzed. The offset error causes the torque of a motor to oscillate and these torque ripples deteriorate the performance of the speed estimator. In order to eliminate ripples in the estimated speed, compensation has been made using a programmable cascaded low pass filter. Results from modeling and experiment verify the effectiveness of the sensorless speed estimator and offset error compensator.