Speed Sensorless Direct Torque Control Of Induction Motors Based On Space Vector Modulation

Compare to the vector control, direct torque control(DTC) technology is also ahigh performance control technique for AC motors, which has many advantages suchas the simple structure, good dynamic torque response、strong robustness and easy todigital control, etc. But in DTC there are some shortcomings such as low speed torqueripple、stator flux round distortion、switching frequency not fixed and so on. In thispaper, the characteristics of DTC are firstly expounded. Based on the analysis of thebackground and significance related to this study, the research development status oftorque ripple reducement and speed identification are discussed.By presenting the mathematic model and the coordinate transformation of theinduction motor, the principle of the DTC system is analyzed, the cause and factor ofthe torque ripple in DTC system is deeply studied, the calculation of expected voltagevector and space vector modulation (SVM) technology are detailedly elaborated, themethod of speed identification based on model reference adaptive system(MRAS)approach is deduced, and the induction motor speed sensorless direct torque controlsystem using space vector modulation technology is researched.This paper particularly studies the methods of speed identification based onMRAS and induction motor direct torque control using expected voltage space vectormodulation.The simulation models of traditional DTC system and the improved DTC systemare built in the Matlab/Simulink. By simulating and contrast analysis, the simulationresults indicate that the SVM can greatly reduce torque ripple, and make the statorflux track better approximate circular, the speed simulation results prove thefeasibility and validity of speed identification based on MRAS.This paper designed a DTC system using the dsPIC30F6010A which isspecialized in the motor control. The hardware and software are designed respectively.In the hardware, the whole design is firstly expounded, and the hardware circuit ofcontrol system is designed in detail. The software design introduces the overall designidea of system software at first, then designs the flow charts of main program、external fault interrupt handler subprogram and timer interrupt service subprogram.Finally, the experimental platform is introduced, and the experimental results areanalyzed. The experimental research further indicate that space vector modulation technology can improve the low speed performance and system dynamic and staticresponse of DTC system, and this method has good application prospects.