| Due to the development of industrial production and energy demand, as a high-performance AC drive control technique, Direct Torque Control (DTC) technique is highly valued around the world. Compared to Vector Control technique, DTC technique eliminates the need of many complex vector transforms and overcomes the dependency to rotor parameters. Although the traditional DTC strategy the structure has a simple structure and fast dynamic response, due to the use of pure integrator stator flux observer, the inevitable DC disturbance of the flux observer will lead to the error accumulation in pure integrator, thus, the observation precision will decline. Therefore, a modified DTC strategy is deeply studied and analyzed in the paper, the main research works are as follows:Firstly, the mathematical model of asynchronous machine is built and the basic theories of DTC are elaborated in the paper, then two kinds of modified flux observing methods are designed and analyzed based on the analysis of traditional flux observing methods, and the respectively simulation is analyzed in the paper. In addition, the paper adopts a speed sensor-less strategy based on Model Reference Adaptive (MRA) to identify the rotor angular velocity through analyzing and comparing the advantages and disadvantages of many speed estimation strategies. Furthermore, basing on the analysis of traditional PI Control DTC strategy, the paper proposes that Variable Structure Control (VSC) substitutes PI Control, so that the modified DTC system based on VSC theory will have better dynamic responses and robustness for the motor parameters.Finally, in order to prove that the modified DTC system based on Variable Structure Control Theory is valid and feasible, the simulating model of the modified DTC system is built by using Matlab/Simulink program based on the analysis of traditional Space Vector Pulse Width Modulation Direct Torque Control(SVPWMDTC) system, and the paper carries out simulink verification and analysis. |
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