Research On Direct Torque Control Of Asynchronous Motor Based On Sliding Mode Control

In the field of AC drive,direct torque control technology(DTC)has the advantages of simple structure,good dynamic performance,and less involved motor parameters.It is another kind of AC speed control method with broad prospect after vector control,so it has received widespread attention.However,the traditional direct torque control's torque and flux ripple is large,the switching frequency is not constant,the motor parameter changes or external perturbation system robustness and other issues limit its application.Variable structure control system with sliding mode is a nonlinear control method,because of its sliding mode dynamic can be designed,the system parameters and external disturbance has a strong robustness of the advantages.Therefore,the variable structure control system with sliding mode algorithm is used in the DTC system of induction motor as the starting point to suppress the torque and flux's ripple and improve the robustness of the system.The mathematical model of induction motor is given in this article,the basic principle of asynchronous motor DTC is introduced,and the root causes of traditional DTC torque and flux ripple are analyzed.Secondly,the basic structure and design method of the sliding mode variable structure control system,the reason and the weakening method of the system buffeting are studied by using the sliding mode variable structure theory.Then,an improved reaching law is given,and a new type of sliding-mode variable-structure controller based on the improved reaching law is designed for the second-order system.The sliding mode controller based on the constant velocity reaching law is designed to suppress the chattering aspects of the comparative analysis.Then,an asynchronous DTC system based on torque and flux sliding structure is designed.The main idea is to replace the hysteresis regulator in the traditional DTC with the newly designed torque and flux sliding mode controller.SVPWM instead of the voltage switch vector selection table for power inverter control.Finally,based on the above research,the simulation model of SVM-DTC system based on torque and flux sliding mode variable structure is established by Matlab/Simulink.The simulation results show that the torque ripples of the system is reduced from 75%to 9.4%,the torque ripple reduced 87.47%respectively.Compared with the traditional DTC system,the stator flux trajectory is more similar to the circular trajectory and the ripple is also effectively suppressed.When the frequency of the switching device is constant,the system exhibits strong robustness to the parameter change and the external disturbance.