Research And Application Of Direct Torque Control Strategy For Permanent Magnet Synchronous Motor Drives

Permanent magnet AC servo system has been the development trends with high location accuracy, running stability in low-speed, fast response time, high overload ability and high reliability. Direct Torque Control (DTC) is an advanced AC drives control principle where inverter switching directly controls the motor variables: flux and torque. DTC technology has been widely researched for the characteristics of briefness, robust, excellent dynamic response. The strategy of DTC for PMSM was researched and implemented in this paper.The organization and characteristic of PMSM was introduced, and the mathematics models in various coordinate were set up. Then a method of the DTC for PMSM with constant switching frequency was presented in this paper. The whole work of the paper contains:(1) The mathematics models in various coordinate were set up by the analysis of the organization and characteristic of PMSM. It gives a further study of the direct torque control of PMSM.(2) A method of the DTC for PMSM with constant switching frequency was presented. Simulation result indicated that system performance was improved by the improvement of switching frequency. Because the stator flux linkage is calculated from the integration of the difference between the machine input voltage and voltage drop across the stators resistance, and the input voltage is obtained by synthesizing the DC-link voltage and the switching mode of the inverter. The accurate calculation of the input voltage and the compensation for the DC-offset error and the variation of the stator resistance are important factors in practical implementation of the integration since they can cause a drift in the stator flux linkage trajectory and furthermore deteriorate the quality of torque control. The methods of PI resistance estimation and nonlinear perpendicular flux observer with compensation feedback were carried out. By the theory analysis and simulation, the proposed strategy was proved to diminishing the torque ripple especially in low speed rang.(3) The experience platform was designed based on Digital Signal Processor TMS320LF2407A. The hardware includes main circuit, measurement circuits, protection circuits and control circuits. The software includes main program, timer interrupt program and SCI interrupt program. The methods which were presented in this paper such as SVPWM, stators resistance estimation, flux linkage observation were implemented and verified.(4) Finally, the future works and developments are introduced.