Research on the method of direct torque control of permanent magnet synchronous motor switching frequency constant

Different from the decoupling idea in the traditional vector control, the direct torque control replaces the rotor flux orientation with the stator flux orientation, cancels the rotation coordinate transformation, and has the advantages of simple control structure, fast operation speed, and strong robustness. The non-constant switching frequency is a major defect of the PMSM-DTC system. Aiming at this problem, this paper proposes a method to keep the switching frequency constant. That is, the hysteresis band is determined by online calculation, the action time of each vector in the switch table is controlled by two adjustments to the hysteresis range, and the switch sequence is limited. Finally, an output spectrum similar to the seven-segment SVPWM is achieved to keep the switching frequency constant.