Research On Direct Torque Control Methods For Permanent Magnet Synchronous Motor Based On Optimization Of Torque Ripple

Permanent magnet synchronous motors(PMSM) lies in a very important position in the nation economy of China for or its advantages of high efficiency, high power density and high torque-inertia-ratio.Direct torque control(DTC) is another high performance control method of PMSM after field oriented control. It possesses excellent dynamic performance coexisting with the weakness which greatly restricted it’s development and application such as big torque ripple and poor low-speed property. This paper focused on non-salient pole type sinusoidal PMSM and made a study of PMSM DTC methods with different basic theory and technical route based on optimization of torque ripple by theory analysis and computer simulation. The main research issues are as follows:The research of PMSM DTC at home and aboard is combed and the coordinate transformation common used in analysis and mathematic model of PMSM is introduced. Two generations of traditional DTC and DTC with no flux loop and main technical route of Bang-Bang control and SVM are summarized and compared.Sector subdivision could be used to reduce the torque ripple. The control result of three sectors subdivision methods of six, twelve and eighteen are comparatively analyzed. The distinction of different methods is discussed and the impact of dynamic performance and inverter switching frequency between three sector subdivision methods is study.The generation of reference voltage vector is very important in PMSM SVM-DTC and generating the reference voltage vector according to flux error is common used at present. Acting characteristic of statorvoltage vector to torque angle and flux are analyzed and a SVM-DTC method based on torque angle is proposed. The methods use PR regulator with better performance in AC system to replace traditional PI regulator and the simulation results demonstrate the correctness and effectiveness of the proposed method.A new DTC based on SVM of permanent synchronous motors without flux loop was presented by learning from the use of SVM in traditional DTC. The method generates the reference voltage vector combined with the characteristic and demand of the DTC without flux loop. The simulation results shows that the method can reduce the amplitude of stator flux linkage and torque ripple further, and the power factor is higher.