Research On The SVM-DTC Control Theory For Induction Motors

Direct torque control(DTC)technique has developed since the 1980, It is a newly high-powered AC drive control technique after the vector control technique.DTC directly calculate and control the torque of AC drive in the stator reference frame.By using stator field-orientation,the optimum switching mode is achieved to control the inverter.DTC suffer the widespread concern and the quick development because of it's novel control thought,manifest system construction and well stationary and dynamic characters.In this thesis the author made a profound and broad study on the design of speed observer and stator flux observer and the digital realization of system.Speed sensorless asynchronous motor system of direct torque control has been introduced by high performance digital signal processor(DSP) of TMS320F2812.Because of the limitation of the classical observer method of stator flux,the observing precision of the stator flux observer must be high,a new adaptive stator flux observer is proposed.With this observer,the stator flux and the speed can be also observed.The robustness to parameter variations and good performance are fully verified by the simulations.Based on the full order flux observer,according to the Lyapunov'theory,the adaptive schemes of speed observer are designed successfully.At last,the author applied a simple speed estimator combined with the flux observer in the direct torque control system.The defect of the classical DTC is researched,a new tactic of Direct Torque Control based on space vector modulation is proposed. Performance of DTC system is improved.An improvement can be obtained adding a new DTC algorithm based on the application of the space vector modulation(SVM) to DTC.At each sampling period,the voltage vector is synthesized two of voltage space vectors and zero voltage space vectors.By this means,the torque ripple is reduced. Simulation and experiment results show that these methods above-mentioned can hold dynamic performance of the basic DTC, weaken the torque ripple and electromagnetic noise greatly.Furthermore, the methods are very easy to realize and have improved accuracy of the observation.The system is implemented on a Digital Signal Processor (DSPTMS320LF2812).The real-time controller software is written by C language,and the research of digital realization and the software design are carried out.