Adaptive perpendicular flux observer with compensation feedback for direct torque control

To resolve the problems of direct current drift and inaccurate estimation of the stator flux linkage at very low speed under direct torque control (DTC) using conventional flux observer, a new adaptive perpendicular stator flux observer with compensation feedback suitable for DTC application was presented. As the back electromotive force (EMF) under DTC operation is not continuous but discrete, a low-pass filter block was set behind the back EMF block to make the back EMF signal continuous so that the dot product of flux vector and back EMF vector was calculated. Compensation feedback flux was automatically adjusted through a proportional-integral (PI) regulator by checking the perpendicular degree of flux vector with back EMF vector. Simulation results verified that the proposed observer could accurately estimate the stator flux linkage when the motor ran at very low frequency of 0. 3 Hz and at the rated frequency of 100 Hz. The high performance operation for permanent magnet synchronous motor DTC using the proposed flux observer was achieved with satisfaction.