Study on the direct torque control of permanent magnet synchronous motor drives

The theoretical basis of the direct torque control (DTC) of permanent magnet synchronous motor (PMSM) drives is firstly explained in this paper. It is proven that while the amplitude of the stator flux linkage is kept invariant, the electromagnetic torque of a PMSM is directly proportional to the sine value of the angle between the flux linkages of the stator and rotor (power angle). Therefore, precise torque control can be achieved by controlling the instantaneous speed of the stator flux linkage with its amplitude kept constant, which is yet to be fulfilled through the agency of proper selection of the voltage space vector generated by an inverter and its acting time. Secondly, DTC for PMSM with circular and hexagonal flux linkage trajectory was investigated by simulation and compared with the traditional id=0 current vector control, which further demonstrates that the DTC possesses much faster dynamic torque response than other control strategies.