Research On Special Convertor Based On Direct Torque Control

The direct torque control theory is a kind of new control method after vector control theory in AC control field. The torque of motor is calculated and controlled in the stator reference frame coordinate using the voltage space vector. By using stator field orientation, the optimum switching model is achieved to control the flux and the torque of motor precisely and quickly when better quality steady-state performance is produced.Now, in the centrifuge industry, the current convertor is adopted, which has good performance, but its parameters are complex and it costs higher. In order to reduce company's expenditure and enhance control performance to the motor, the special convertor is designed by using the DTC control method in the paper, because of the advantage of DTC.The paper starts by reviewing the basic math model of an asynchronous machine and of a PWM inverter using the space vector theory. It also analyzes the principle of induction motor direct torque control and the composition of the DTC system. A simulation system is developed using MATLAB/Simulink software package for the purpose of validating machine control system with a direct torque. In the paper, parts of the simulation system are introduced, including the 3/2 transform model, flux observation, torque observation, torque regulator and flux regulator, sector selecting, switching table etc, and then the results were simulated indicated a performance at increasing-load and decelerating. Simulation results show that the approximate circle flux control system has good dynamic and static performances and has proved the feasibility and correctness of this method.According to the method and results of simulation, the hardware circuit of the whole system are designed, including the main circuit (the single-phase rectifier, filter, the circuit of breaker, the circuit of current prevented, convertor) and control circuit (DSP, driver and insulator, the giving circuit and display), it also gives the choice of the elements and the figures of hardware circuit of parts of the system. Last this paper has introduced the soft program of the DTC system at the pain of TMS320LF2808 DSP setting, the software of the control system in C program has accomplished the DTC algorithm design. This software has realized functions of the sampling of stator phase current, calculating of the phase voltage, the observing of stator flux and the output of switching signal etc. After debugging hardware and software respectively, the unitary experiment has been accomplished. The control aim is accomplished by changing the speed of the motor according to the frequency and running steady.