Research On Direct Torque Control Strategy For Asynchronous Motor

Direct torque control technique (DTC) is a new high-performance AC frequencycontrol technique, which followed field-oriented control technique. However, DTC hassome disadvantages on torque ripple and flux linkage trajectory, which makesdifficulties in development and industry application. As for many disadvantages liketorque and flux linkage ripples, high current harmonics and variable switchingfrequency in conventional switching-table direct torque control scheme，this papermainly focus on the improvement research on stator flux linkage observer and controlstrategy on the based of a profound and broad study on the DTC theoretical analysis.Directly, the observer accuracy of stator flux influences the performance of DTCsystem. Based on making deep analysis on the limitation on the traditional stator fluxlinkage observer models, a few common improved methods are introduced in order tosolve problems of DC drift and error accumulation in voltage model. On this basis, thepaper design the stator flux observer model based on the amplitude and phasecompensation to improve the flux observer accuracy.With respect to researches on control strategy, based on the analysis of thetraditional DTC system performance, DTC based on vector subdivision and DTC basedon space vector pulse and width modulation (SVM-DTC) are proposed to solveproblems of torque ripple and not fixed switching frequency and effectively improvesystem performance. Then, the compared the traditional DTC, the vector subdivisionwith the SVM-DTC by using Matlab7.6/Simulink to verify improvement strategies caneffectively reduce the torque ripple and current harmonics and make the inverter toobtain the fixed switching frequency.Finally, the thesis designs direct torque control variable speed system based on thecontrol core of a digital signal processor TMS320LF2407A and the control object ofinduction motor. The experiment verifies the correctness and effectiveness of thetheoretical analysis.