An Study For Decrease The Torque Ripple Of Direct Torque Control System For Induction Motor

The induction motor has the advantages of simple structure,low price and strong environmental adaptability,and it occupies a very important application position in industrial and agricultural manufacturing,military field and so on,by the same time,the research on the speed control system of induction motor has attracted much attention.Direct torque control as a new AC motor control technology,with its control directly,fast response and other advantages,have obvious advantages than other control strategies.In this paper,the induction motor is selected as the research object,and the direct torque control system based on the circular flux linkage is modeled,in addition,given the analyzed and the improvement scheme for the problem of the large torque ripple,so as to achieve the optimization of the control system.In the traditional direct torque control system,the selection of the voltage vector is affected by the width of the hysteresis comparator,and the vector voltage can only be selected from a limited number of voltages during each sampling period,which caused the problem such as the switching frequency is unstable,and the voltage vector is not the optimal value.In this paper,to achieve the improvement of the system,combined with space vector pulse width modulation technology,treat the motor and inverter as a whole,achieving a smooth adjustment of the stator flux,while reducing the torque ripple by making the motor flux linkage amplitude remained constant.Given the compensation measures in order to solve the problem of time spillover in SVPWM system,and the compensation coefficient k is determined by simulation experiment.In order to obtain more accurate voltage space vector to meet the requirement of torque flux linkage,this paper reconstructs the flux linkage and torque controllerwith the idea of Deadbeat Control,the expected voltage vector is obtain by analyzes and calculated the requirements of torque deadbeat and flux deadbeat,and used it as the input to the SVPWM module to control the motor,so that the actual torque and flux can effectively track the given torque and flux on the next sampling period,reduce the fluctuation caused by the error.At the same time,a new control scheme is proposed by analyzing the effect of stator voltage drop on the expected voltage value.And verify its effectiveness by analyzing the error value.The direct torque control system model of induction motor is established in MATLAB/Simulink software environment.The improvement scheme is presented in the simulation model by create a new module.Through the comparison and analysis of the simulation results of electromagnetic torque and stator flux are made before and after the improvement,proved that the stator flux trajectory and the motor torque ripple are improved obviously in the improved direct torque control system,and verified the feasibility of the improved control scheme.