Induction Motor Direct Torque Control System Of Stator Flux Observer And Speed Identification Of Research

Direct torque control (DTC) system of speed sensorless induction motor, which with advantages such as novel control thought, simple algorithm and excellent performance, has got wide attention and development. Based on deeply and extensively study on the veracity of stator flux orientation and the accuracy of speed identification, which affect the performance of direct torque control, a new stator flux observer method is proposed, and conventional model reference adaptive system speed identification is improved in this dissertation.According to the limitations of conventional stator flux observer, a new observer based on sliding model observer is proposed in this dissertation. The method simplifies the structure of observer by applying sliding function to replace the state of stator current equation of the anti-EMF, and uses the continuous function instead of switching function to reduce the observer jitter, and introduces the low-pass filters with feedback to compensate the amplitude and phase error of pure integral. The sliding model observer is robust to the variation of stator resistance because it has no relation with stator resistance. Additionally, the new observer has advantages of simplied hardware circuit and the accuracy of flux observation for its low sensitivity to the measurement error of voltage.In order to overcome the defects of the precision of speed identification being effected by stator resistance and pure integration, the dissertation proposes an improved MRAS. Firstly, a high pass filter is introduced to eliminate the effects of pure integration, and low filter's cut frequency is adjusted basing on fuzzy logic. Secondly, a method of fuzzy logic based online stator resistance adjustment is adopted to decrease the influence of stator resistance variation.The simulation model of proposed design schemes are built up with Matlab6.5/Simulink, and the results of simulation indicates that the proposed observer and the flux observer can ensure the speed control system being stable in its full speed range and also in good precision.