The Research On Stator Flux Estimation In Direct Torque Control System Of Permanent Magnet Synchronous Motor

Direct Torque Control (DTC) is a new kind of AC motor control technology with high performance. In recent years, DTC of permanent magnet synchronous motor (PMSM) has become the research focus in the field of AC servo. Traditional DTC has the disadvantages of large flux and torque ripples and bad performance in low-speed region. Moreover, the accurate observation of the stator flux is very important for DTC system. Therefore, this thesis focused on the research of DTC strategy for Surface PMSM (SPMSM) and new methods of stator flux estimation.To reduce the flux and torque ripples and improve the steady state performance in the traditional DTC system, DTC based on space vector modulation (SVM-DTC) was adopted for PMSM in this paper. The basic principle and structure of SVM-DTC system of PMSM were analyzed in detail. Then the simulation platform and experimental platform were designed. Through simulation and experiments, SVM-DTC, traditional DTC and vector control (VC) were compared, and the results indicate that SVM-DTC can effectively inhibit the flux and torque ripples, improve the steady performance while maintaining the characteristic of fast response, and has the basically the same performance with VC.Then based on SVM-DTC system of SPMSM, two new stator flux observers were put forward to improve the dynamic and static performance and robustness against parameter variations. In the first method, an adaptive stator flux observer with stator resistance estimation was designed in two-phase stationary coordinates. In the second method, an adaptive stator current observer in two-phase rotating coordinates was designed for online identification of stator resistance and stator inductance, and the estimated values were further used in full order stator flux observer. According to Lyapunov stability theory, the feedback gain matrix and adaptive laws were designed to ensure the stability of the proposed adaptive observers. Simulation and experimental results confirmed the effectiveness and robustness of these two new stator flux observers.