Research On Sensorless Direct Torque Control System Of Asynchronous Motor With Stator Resistance Identification

Direct Torque Control(DTC)system of Asynchronous motor has the advantages of simple structure,fast response of torque and low dependence on motor parameters.However,it is necessary for traditional DTC system to install speed sensors,which leads to more system cost,reduced reliability and poor environmental adaptability.Taking the sensorless DTC system based on Extended Kalman Filter(EKF)algorithm as the research target,this paper conducts research on identification of motor speed and stator resistance and optimization of torque ripple.The mathematical model of asynchronous motor in the?-?stationary coordinate is derived firstly and then the principles of DTC technology are presented.For the purpose of optimizing the torque ripple,the change rate of electromagnetic torque is derived and problems of traditional DTC system are analyzed including unbalanced change rate of electromagnetic torque,varied switching frequency and exceeding the limit of torque hysteresis comparator.Replacing the torque hysteresis controller,a constant switching frequency controller is presented to solve these problems.The principle of the EKF algorithm is detailed.Based on the state equations of I_s-?_s-?_r a sensorless DTC system based on EKF algorithm is designed.Then,the influence of stator resistance change on the sensorless DTC system during motor operation is analyzed.In order to solve this problem,the model of EKF algorithm is adjusted.The stator resistance is identified as the state quantity and fed back to the EKF algorithm,which avoids the effect of stator resistance disturbance on the speed sensorless DTC system.The sensorless DTC system with stator resistance identification is simulated in Matlab/Simulink.The results of simulation show that the improved torque controller can reduce the torque ripple and the control system can identify stator resistance accurately and maintain the speed estimation precisely.Finally,the hardware and software of the sensorless DTC system are designed and the experimental platform is built and tested to operate experiments.The results verify the effectiveness of the control system designed in this paper.