Research And Realization Of Strategies In Asynchronism Motor Direct Torque Control Based On Dsp

Compared to Vector Control Direct Torque Control (DTC) has been widely studied and used during recent years due to its simple control structure and excellent performance.The paper mainly discusses torque ripple, flux observer, startup method and weaken flux control in asynchronism motor direct torque control system.The large torque ripple at low speed are the problems of ST-DTC.So the scholar in our country and abroad has put forward many strategies to solve the problems.One method is ST-DTC based on torque prediction. Another method is using SVPWM instead of switch table. Research has proved the control strategy based on SVPWM can solve the two problems effectively. This paper uses the SVPWM method that can calculate the reference voltage space vector from the torque and flux errors; the method is called SVM-DTC.The experiment results show SVM-DTC can reduce the torque ripple of the whole speed range, improve the waveform of stator flux and current, reduce the noise and the vibrate of running. This paper gives a detailed analysis of flux observer, and focuses on the two u-n models which can run in the whole speed range. The paper gives analysis of choosing the state variable in flux observer, calculating equations set in discretization and the analysis of discretization method and the step of discretization.The experiment results show that the u-n model can accurately observe the flux of the whole speed range.This paper designs two startup methods. One method is flux priority, another is ramp function. The experiment results show that the flux priority method not only can improve the starting performance, but also reduce the ripple of torque and flux; the ramp function method could restrict the startup current and use in governor, positive and negative speed, stopping.This paper introduce the principle of weaken flux control and draw up two schemes. The simulation results show that the two schemes both can work in weak magnetism. The open loop given method is simple and effective, which finds out the given value of flux according to the speed. The scheme of close loop tuning contains PI regulator, so we need tune the PI parameters.The experiment is achieved on the asynchronism motor platform with DSP chip TMS320LF2407A as control core for ST-DTC,TP-DTC,SVM-DTC.The experiment results show SVM-DTC can reduce the torque ripple and improve the waveform of stator flux and current.