Ac Induction Motor Direct Torque Control, Low-speed Performance Optimization

There exists some problems of flux ripple and torque ripple in traditional Direct Torque Control(DTC). Below 30% of rated velocity, these problems will make the performance of speed control to descend badly, even lost control, which limits the scope of application of DTC. It is the key of widening the scope of application to improve the performance at low speed.The paper analyzes systemically and completely the existing problems at low speed of DTC, analyzes the reasons, and indicates the direction of improving, and puts forward a new method of observing and compensating stator flux based on U-I model in order to improve the performance at low speed. In the method, Low-pass filter replaces traditional U-I model, and the cut-off frequency can adaptive with the bias and stator frequency, so the problems about bias and DC initial value can be restrained, and compensates the subsequent error of phase with Fuzzy controller; At the same time, puts forward a new method of pure soft to compensate dead-time, without changing hardware.In the environment of Matlab, uses the power system block to build a simulink model. Compared the traditional DTC and improved DTC based on the simulink results, the results shows that the improved DTC has a good performance at low speed, which proves the validity of the method put by the paper.Finally, a experimental system of DTC is designed, a chip of TMS320F240 is chose as main chip to construct the hardware system, and uses assemble language and C language to programme to realize DTC.