An Asynchronous Motor Direct Torque Control System Based On SVPWM And Full-Order State Observer

Ac speed regulation control theory developed from the voltage-frequency control, theslip frequency control to vector control and direct torque control, the control performance ismore and more outstanding. With the advantage of direct control method, fast control speed,better control effect, the direct torque control has become a high performance speedregulation technology in ac drive field, and obtained widespread promotion and application.however, the pulsation of the torque, current and flux, the frequency of the switching, and theaccuracy of the stator flux linkage observation have been hindering the asynchronous motordirect torque control to further improve its performance.Based on analysis of the direct torque control system, the article proposed aasynchronous motor direct torque control strategy based on space vector pulse widthmodulation (SVPWM) to solve the existing problems. And designed a kind of full-order stateobserver of induction motor, its state variables is stator current and stator flux. Its applicationto the direct torque control system to improve the observation precision of the stator magneticchain in low speed. The new direct torque uses PI controller instead of hysteresis controller oftraditional control system to control the stator flux linkage and torque, uses SVPWMmodulation technology to obtain the desired voltage vector to control inverter, and moreaccurate full-order state observer is used to replace the U-I model flux observation of thedirect torque control system.Theoretical analysis indicates that the new system can maintain constant stator fluxamplitude, more accurate flux observation and flux trajectory is nearly circular. The controlperformance of flux and electromagnetic torque is smooth, the new system can effectivelysolve the traditional direct torque control’s disadvantages.In order to verify the correctness of theoretical analysis, this paper use simulinksimulation platform, respectively, set up the simulation system of the traditional direct torquecontrol and the new system. Through the reasonable parameter settings of the system, weobtained the simulation waveform of two systems. The simulation results show that the newsystem can effectively reduce the torque ripple and current distortion, the flux linkage hashigh accuracy observation and fast convergence speed. Compared with the traditional directtorque control system, the new system’s control performance is improved obviously in lowspeed.