Research On DTC Of Induction Motor With Low Torque Ripples

DTC is a high-performance frequency control of induction motor which developed followed vector control in the mid-80s of last century. DTC has novel control thinking, simple and direct control structure, a clear physical signal processing concept and a rapid torque response. Although DTC has indisputable advantages compare with vector control and gradually becoming more mature, as a new theory, it has imperfections. If the shortages are not improved, its large-scale application will be limited. For example, influences caused by the changes of stator's resistance in low-speed range, torque ripples caused by fast dynamic response, etc. these weaknesses affect the control performance of DTC.Based on the detailed analysis of the basic principle and composition of DTC, the paper constructed a DTC system model of asynchronous motor in Matlab, reached and analyzed the conclusion. Focus on torque ripple of DTC in the low-speed range, two main reasons are summarized. Considering the influence of voltage space vector on the magnitude of stator flux and torque in direct torque control for asynchronous motor, a new flux section subdividing method and a comparative analysis of two flux section subdividing methods is presented. The simulating result proves that the improved 12 section of flux section subdividing method has better control performance than the conventional one when the flux can not been observed accurately. It can improve the flux trajectory and reduce the torque ripples effectively.Matrix converter is a new AC-AC power converter with an excellent input and output characteristics. MC is suitable for application in the field of AC speed adjustment because it can make the energy bidirectional flow and control power factor. This paper analyzes the structure, current-change mode, modulation strategy and the 27 switching states of matrix converter. Switching table of MC-DTC is presented combining DTC theory. The integration between matrix and direct torque control is realized by constructing model in Matlab/Simulik.