Low-speed Performance Study Of Direct Torque Control System Of Asynchronous Motor

As a new control method, Direct Torque Control method has its advantage because DTC system has robust performance and simple structure comparing to Field-orientation control system. But Direct Torque Control system can hardly have as broad as the speeds range which Field-orientation system can have. It is because that DTC system can not have big load capability and there are torque pulses in it. This paper has made a further research about low-speed problems of the Direct Torque Control system.The defect of the classical DTC is researched deeply, this paper propose two novel methods which can improve DTC system low-speed performance. One method is a novel compensation method of stator flux estimating to improve Direct Torque Control Low-speed Performance. Using low-pass filter to replace the integrator, compensate the value of the flux with close-loop feed back and compensates the subsequent error of angle with Fuzzy controller, not only improve the estimation of stator flux but also can reduce the effect of stator resistance voltage drop. The other method is a novel method which combines fuzzy control with low-pass filter compensation. According to the relationship between real value and estimated value of the stator flux. The compensatory formulas of the estimated flux linkage and its principle block diagram were presented. Using this method control converter's output. The simulation results showed that proposed two methods give satisfied estimation of stator flux and improve direct torque control system good robust. The performance of low-speed have been improved in direct torque control system, confirming the validity of the method.Finally, we have experimented by digital fuzzy DTC control system based on the TMS320LF2407A chip. That is to say, we can improve the low-speed performance of the system by modifying software. The experiment results verify the validity of the proposed scheme in this paper.