Research On DTC System For Asynchronous Motor Based On SVPWM

Direct Torque Control, following the vector control technique, is an emerging technique in the field of AC Motor speed control. Using the space vector analysis method, the DTC technique calculates and controls the torque and flux linkage in the stator coordinate system in order to obtain higher dynamic torque performance. Comparison of vector control, DTC eliminates the need of complex vector transform, overcome the dependency to rotor parameters, and has an advantage of fast torque response. However, the asynchronous motor traditional DTC system has the problem of torque, flux linkage and current ripple and inconstant switching frequency. To solve these problems, this paper brings forward a novel DTC system based on SVPWM in the base of traditional DTC.This novel DTC system makes SVPWM and DTC into a good combination. The motor and PWM inverter are seemed as one controlled object, so that the motor can obtain a constant magnetic field similar to the ideal circle and at last, solving the problems of torque, current, flux linkage ripple and inconstant switching frequency. In the process of writing paper to do following work:According to motor theory and coordinate transformation principle, build up the mathematical model of asynchronous motor in the stator alfa-beta two-phase orthogonal stationary coordinate system. The motor torque and flux linkage can be observed through flux linkage model, torque model and motion equation of motor.Design the PI controller and transform the torque and flux linkage error signal into the reference voltage. Through the coordinate transformation the reference voltage is transformed into the directive voltage that the SVPWM module required to control the SVPWM module.SVPWM is a key module to motor input control voltage, it designs the method of synthesize the wanted voltage space vector, determines the vector section. It also calculates the time-range of switch-on and the time when the switch-on.Through theoretical analysis and design of various modules, build up the simulation model of inverter part of control system in MATLAB / SIMULINK simulation toolbox. By setting the reasonable simulation parameters, electrical parameters, as well as PI control parameters for PI controller. Then the Simulation of the system is operated in order to theoretically verify the correctness of the system design.The simulation results prove that the DTC technique based on SVPWM can effectively improve the DTC system control performance. Reducing the flux linkage and torque ripple, making the inverter work in the constant switching frequency. In the end of paper, it concludes the work have done and put forward the future focus and direction.