In the process of motor operation, the speed of direct torque control is very fast in a wave load cycle, but the change rate of stator flux amplitude is small. Therefore, in the analysis process, the stator flux amplitude rate of change can be regarded as a fixed value, and only the angle between the stator and the rotor flux can affect the electromagnetic torque. That is to say, in the process of synchronous motor operation, the torque angle can be changed to change the magnitude of flux torque.