Research On Direct Torque Control System Of Asynchronous Motor Based On SVPWM

Direct torque control is a new kind of frequency control of motor speed technology,which experienced three phase that a hexagon flux direct torque control, round flux directtorque control and direct torque control based on SVPWM. Hexagon flux direct torquecontrol is only suitable for the occasion because it exists large flux linkage and torque rippleand low switching frequency at low speed; Circular flux direct torque control due to the fluxand torque hysteresis regulation, which leads to torque and current harmonic component isbigger, the switching frequency is not stable; Based on SVPWM direct torque controlaccording to the error of stator flux and electromagnetic torque, by controlling the time ofvoltage space vector and given order, make the voltage space vector is close to rotate circulartrajectory, so that the motor flux trajectory approaching round, because the output voltagevector considering the error of stator flux and electromagnetic torque size and the direction, soat the same frequency can effectively reduce the torque and flux ripple.Because the circular flux direct torque control exists large torque ripple, current distortionis serious and switching frequency is not fixed, this paper from the mathematical model ofasynchronous motor in the stator system, expounds the basic principle of direct torque controlsystem and space vector pulse width modulation (SVPWM) technique’s principle andrealization method, a detailed analysis of the relationship between voltage space vector andstator flux and electromagnetic torque, analyses the difference between the circular flux directtorque control and direct torque control based on SVPWM.According to the principle of circular flux direct torque control and based on SVPWMdirect torque control, research and simulation the circular flux direct torque control and directtorque control based on SVPWM on the platform of MATLAB. The simulation results showthat the circular flux direct torque control is suitable for low speed occasion, and direct torquecontrol based on SVPWM compared with the circular flux direct torque control can effectively reduce the current harmonics and torque ripple of the control system, and the switchingfrequency constant.On the basis of theoretical analysis, design of asynchronous motor variable frequencyspeed control system hardware and software system, the system hardware consists of the maincircuit and control circuit. Main circuit includes inverter circuit, rectifier circuit, starting circuitand filter circuit, each device selection and relevant parameters determined; Control circuitincluding DSP2812control chip, optical coupling isolation circuit, fault isolation circuit,voltage and current detection circuit. Software design of the system is completed under theCCS3.3development environment, mainly complete the voltage, current and speed samplingand SVPWM direct torque control of relevant calculation.The experiment platform fordebugging, comply with the design requirements.