Research On Direct Torque Control Of Interior Permanent Magnet Synchronous Motor

The interior permanent magnet synchronous motor has excellent power factor,high power density and strong overload capability,so it is widely used in industrial fields.At present,the main research directions of motor control technology are vector control and direct torque control.Direct torque control has become one of the commonly used control methods in AC speed control systems because of its simple structure and small dependence on encoder position accuracy.However,due to the use of hysteresis comparators to directly control the torque and flux linkage,the controller performance is degraded,resulting in insufficient switching frequency,large torque and flux pulsation.Therefore,the thesis combines the structural characteristics of the interior permanent magnet synchronous motor to carry out optimization research on the existing problems.Firstly,the development history of three speed control methods are introduced,and the control effects are analyzed in detail.The mathematical model and transformation method of the interior permanent magnet synchronous motor in three different coordinate systems are derived.The basic control idea of the traditional direct torque control system,after which,the interior permanent magnet synchronous motor direct torque system simulation model was established,and the interior permanent magnet synchronous motor direct torque system with zero voltage vector added to the switch table was carried out.Simulation studies show that the control method of adding zero voltage vector can effectively reduce the flux linkage and torque ripple.In order to reduce the torque ripple at a constant switching frequency,a interior permanent magnet synchronous motor direct torque control scheme based on constant switching frequency is proposed,which compares the output of the PI torque regulator with The fixed frequency carrier signal realizes the constant switching frequency of the inverter.The simulation of the speed,torque and stator current is carried out on the traditional DTC and the DTC control method based on constant switching frequency.The simulation results show that the constant switching frequency is based on DTC has better control effect than traditional DTC,that is,DTC method based on constant switching frequency can effectively suppress current distortion,overcome the problem of large torque,ensure the switching frequency of power device is constant,and retain the dynamics of DTC method.Fast response and robustness to motor parameters.