Comparative And Experimental Research On Direct Torque Control Strategy Of Asynchronous Machine

It is well known that DTC presents some disadvantages on flux linkage trajectory and torque ripple, especially bad performances at low speed in comparison with FOC, which makes difficulties in employment in industry application. In this essay the author made a profound and broad study on the theoretical analysis, stator flux observer and the reduction in torque ripple of direct torque control system. The digital realization of asynchronous machine system of direct torque control has been designed by high performance digital signal processor.As for many disadvantages like high current harmonics, torque ripples and variable switching frequency in conventional switching-table direct torque control scheme, the author mainly focus on his research on stator flux linkage observer and control strategy. After making deep analysis on the limitation on the traditional stator flux linkage observer models, a few common improved algorithms are introduced in order to solve the pure integral deviation problem in voltage-based model. Besides, two forms of hybrid-model stator flux linkage schemes are fully discussed as a high performance observer.With respect to researches on control strategy, three noble algorithms besides the classical one are proposed and summarized in a detail way. They are conventional hysteresis-switching-table DTC (ST-DTC), discreet space vector modulation DTC (DSVM-DTC) and constant switching frequency space vector modulation DTC (SVM-DTC). Additionally, the total performances of later one are better than the formal. Then simulations have been carried out for the evaluation of the proposed control algorithms with high performance stator flux linkage observers. The simulation results show the high accuracy of observers and effectiveness of schemes.At last, the author designs a set of full digital direct torque control experimental platform of asynchronous machine. The experimental system is composed of control circuit based on TMS320LF2407A and power circuit with IPM. All the control software is programmed in assemble language. A large series of experimental researches are tested on the platform. Good control performances are made in such test conditions like zero load, full load, speed response and torque response test situation.