Study on direct torque control of permanent magnet synchronous motor based on observing stator flux linkage

A direct torque control (DTC) strategy based on observing stator flux linkage for permanent magnet synchronous motor (PMSM) was investigated. Traditional DTC can adjust the torque and flux linkage just with only 8 basic voltage space vectors. It has rapid dynamic response, but, it also has the shortcomings: ripple of torque and current, variable switching frequency, and poor performance while low speed. Therefore, a PI controller was used instead of the hysteresis controller and switching table in traditional DTC. The voltage space vector prognosticated by the error of torque for compensating the error of flux linkage is deduced. With space vector modulation (SVM), the error between the estimated and the referenced of stator flux linkage and torque will be accurately compensated by the synthesized voltage space vector. The simulations and experiments verified that compared to DTC of PMSM, DTC-SVM is capable of keeping the excellent dynamic response, also evidently reducing the torque ripple and effectively improving the steady state performance.