Research Of Asynchronous Motor Direct Torque Open-loop Control

With the development of power electronics and motor control chips, the speed controltechnology of the asynchronous motor is developing rapidly which has gone through V/Fcontrol, vector control and direct torque control. Direct Torque Control is a new technology inthe ares of AC speed control which has many advantages such as new control method, simplestructure, direct control means and fast torque response. DTC technology is playing a veryimportant role in the area of motion control.By controlling the voltage space vector, Direct Torque Control can control the rotationspeed of flux, so as to achieve the goal of control motor speed. With the flux regulator and thetorque regulator, DTC can follow the stator flux and the torque so as to control the outputvoltage and obtain fast torque response.In this thesis, Based on the mathematical model of asynchronous motor under the statorcoordinate system. The inverter model based on voltage space vector, the hexagon fluxtrajectory and the principle of DTC are introduced. Four kinds of relationships are analyzedwhich contains the role of voltage space vector in flux adjust and torque adjust, therelationship between the given value of flux regulator and hexagon flux, the relationshipbetween the tolerance value of torque controller and the output torque, and the relationshipbetween the size of the duty ratio and rotational speed. Based on flux regulating principle,DTC can generate circular flux by adjusting the effecting time of voltage.Based on the regulation principle of flux and torque, With the question of how to changethe flux trajectory, the torque ripple and speed by changing the given values of stator flux, thetolerance of torque and the duty cycle in DTC. Direct torque control open-loop simulationmodel is established by the simulation software–Matlab/Simulink, and create the variousmodules of the simulation system. The simulation results show that the greater the flux valueis, the bigger the flux orbit is, greater torque tolerance leading to greater torque ripple and thegreater the duty cycle bring faster speed. The hardware and software of DTC system are designed in this article, part of theexperimental testing has been completed. The hardware system design consists of the maincircuit and control circuit. The main circuit includes the rectifier circuit, the startup circuit, thefilter and inverter ones, Introduce the application of inverter module IPM and designparameters of each device.The control circuit contains control chip DSP (TMS320F28335),sthe isolation circuit, the signal failure circuit and the detection one. The CCS3.3developmentenvironment of software system are introduced. Analysis the main program and theinitialization flowchart. Debugging part of speed regulating system.