Direct Torque Control for Permanent Magnet Synchronous Motor Drive Based on Voltage Space Vector Pulse Width Modulation

　　Direct Torque Control for Permanent Magnet Synchronous Motor Drive Based on Voltage Space Vector Pulse Width Modulation
　　With more and more advanced requirements of social practicality production, the varieties of motor are gradually increasing and the control technologies of modern motor have also been upgraded. Permanent magnet synchronous motor (PMSM) has been widely used in high performance drive applications for its advantages, such as compactness, high efficiency, reliability and suitability to environment. Direct torque control (DTC) which was initially Cast Alnico Magnet applied to induction motor drives has been paid more attractions and dramatically developed with its novel control means, compact system structure and excellent dynamic and static state performances. DTC technology for PMSM drives, however, is not perfect and has some disadvantages. For example, the electromagnetism torque ripple and the low performance of low speed are all very intractable problems, which often lead to the torque and flux ripple and can not obtain optimal control effect.
　　To solve all above problems, the space voltages vector pulse width modulation (SVPWM) strategy of DTC for PMSM is presented. Simulation results show that it can dramatically reduce the torque and the stator flux linkage ripples and it has better dynamic and static state performances, and its fast response, so its function will more stable.Firstly, based on the state of the art review of DTC, the basic theory of coordinate transformation in motor control and mathematical model of PMSM are introduced, and at the same time, the principles of the basic DTC and voltage space vector pulse width modulation (SVPWM) are presented. The control arithmetic of SVPWM http://www.chinamagnets.biz/Alnico/Cast-Alnico-Magnet.php and simulation results are given.Secondly, according to above theories, to solve the problem of the torque and the flux ripples in the DTC system, this paper presents an improved scheme which is based on the space vector of stator voltage pulse width modulation strategy of DTC for PMSM. The simulation model of system is built by the means of MATLAB/SIMULINK. The proposed system is compared with the basic DTC in the aspects of steady state and dynamic state. The simulation results prove the feasibility and advantages of this scheme. Finally, after reviewing many papers about DTC, some problems associated with low speed performance of DTC system are concluded in the paper, and at the same time, several improved methods are proposed. Then how the stator resistance variation affects the system performance is analyzed in the paper. According to above analysis, the stator resistance estimator is proposed to solve the bad effect for the system with the stator resistance variation. Modeling and simulation results further confirm the effectiveness of the proposed stator resistance estimator.