Design And Implementation Of DTC Universal Digital Control System For Asynchronous Motor Based On DSP

Compared with other AC motors, the asynchronous motors has the advantages of simple structure and operational reliability. Meanwhile, it also edges out DC motors due to low cost and small size. Hence, asynchronous motors have been widely used in social production. Among all the controlling methods of asynchronous motor , direct torque control (DTC), which controls the stator flux and electromagnetic torque through stator magnetic field orientation, has drawn great attention from and been widely researched by scholars at home and abroad once put forward due to its following features: novel concept, simple structure, direct control scheme, fast torque response. This paper takes the asynchronous motor DTC as the research object and keys its focal research on the design and implementation of asynchronous motor digital control system based on DTC. The main contents are as follows.1.The mathematical model of asynchronous motors is introduced in detail, in which three common coordinate systems and their transformations are described. This paper also describes the realization of direct torque control with stator winding in star connection in the two-phase stationary coordinate system. It also introduces the influence of eight kinds of voltage vectors on the stator flux and electromagnetic torque in the direct torque control. Comparing the characteristics of the two kinds of flux linkage control, this paper introduces the stator flux observer model based on the low-pass filter.2.The simulation model of asynchronous motor under direct torque control is established in the MATLAB software simulation environment. Functions of rectifier module, coordinate transformation, flux observation and torque calculation module are introduced. The feasibility of the control scheme is verified on the basis of simulation, and meanwhile the control effect of traditional asynchronous motor flux and torque closed-loop control is studied so as to lay the foundation for further practical experiment of direct torque control scheme.3.A set of DTC universal digital control experimenting platform is designed based on TMS320F28335_DSP, and the design of DSP core board, peripheral circuit board and main power board are also completed. With respect to the electromagnetic interference showed in the debugging process of the control platform, this paper ascertain the causes of the interference and the corresponding solutions. On the basis of the successful debugging of each subsystem of the platform,the V/F Open-loop test is carried out based on SPWM modulation. In order to improve the utilization ratio of DC bus voltage, the V/F open-loop experiment under the condition of the injection of third harmonic is carried out as comparison. The reliability and stability of the designed hardware control system are verified by the experimental results under different conditions.4.The experimental research on the direct torque control method of asynchronous motor is carried out, and the experimental analysis and verification of each module of the asynchronous motor DTC are carried out under the condition of pure torque loop and speed loop respectively. The experimental results verify the correctness of the theoretical analysis, the simulation model and the reliability of the hardware control system, and lays the foundation for the follow-up work.