Research On Reducing Torque Ripple In Direct Torque Control System Of Asynchronous Motor

Duty Ratio Control(DRC)technology can effectively improve the torque ripple of asynchronous motor direct torque control(DTC)system during operation and enhance the system control performance.The traditional Deadbeat Duty Ratio Control(DB-DRC)technique has some disadvantages such as poor optimization effect and inconsistent pulsation suppression in different operating states.In this paper,an improved strategy to improve the precision and torque control precision of DB-DRC electromagnetic torque change rate is proposed.Based on the theory of direct torque control(DTC),a direct torque control system of induction motor based on double-hysteresis of electromagnetic torque and stator flux linkage amplitude is established.At the same time,the principle of DRC based on torque deadbeat is analyzed in detail.The relative motion between the stator flux linkage and the rotor flux linkage in the period of the effective voltage vector and the zero voltage vector in the control period is analyzed and calculated to determine the duty ratio of the effective voltage vector.In the traditional DRC technology,the influence of operating status such as motor speed and load torque is neglected in the calculation of the change rate of electromagnetic torque,which leads to the inaccurate result.The improved DRC scheme is based on the position of the stator flux linkage,considering the operating state of the system and improving the calculation accuracy of the change rate of the electromagnetic torque.In addition,in order to further reduce the torque ripple,when the effective voltage vector duty ratio is determined,the instantaneous torque at the end of the control period and the variance of the electromagnetic torque curve in the whole control period are both considered.The modeling and simulation of the improved DRC technology are carried out,and the feasibility and effectiveness of the system are verified by comparing the simulation experiments.Finally,based on digital chip MC56F8257,the hardware and software of the whole control system are designed and tested.The experimental results show that the direct torque control system of asynchronous motor based on improved DRC technology is stable and has good performance.