Flux observer with two-phase-type PLL for sensorless direct torque control of surface mounted PMSM drives

This paper present a novel flux observer using two-phase type PLL (TP-PLL) for direct torque control of surface mounted PMSM drives. The proposed flux estimation combines the voltage-based model and current-based model. The angular position of the stator flux linkage is derived from the integration of the back-EMF using TP-PLL, and the amplitude of stator flux linkage is obtained by solving a set of equations based on the measured currents and rotor flux linkage. The proposed algorithm can significantly alleviate the dc-offset problem on the pure integrator, and eliminate the magnitude error problem associated with the conventional low-pass filter. The simulation and experimental results confirm the validity of the proposed method.