In recent years, multilevel technology has become an effective and practicalsolution for high-voltage high-power application field. As described in manyliteratures, by using multilevel technology, the voltage stress on switches will bereduced, the shape of output waveform will be improved and the rate of voltageand power can be increased too. Diode-clamped three-level inverter is the mostwidely used and investigated topology at present. Direct Torque Control (DTC)is an advanced AC drives control principle where inverter switching directlycontrols the motor variables: flux and torque. DTC technology has been widelyresearched for the characteristics of briefness, robust, excellent dynamicresponse.This paper will focus on the study of direct torque control of inductionmotor drive based on diode-clamped three-level inverters. The whole work ofthe paper contains:(1)By the analysis of a three level inverter and direct torque control, themathematic model of three-level inverters and that of induction motors has beenconstructed. (2) The problems existing in the system of direct torque control based on athree-level inverter has also been studied. By all these above, it gives a furtherstudy of the relationship of the AC drive and three-level inverters.(3) On the basis of the concept of space vector, the basic theory of DTC isanalyzed. Also a representative DTC strategy improving operation performanceof induction motors is introduced. The performances of the strategies areanalyzed with the simulation results.(4) In this paper, it introduces the principle of Direct Torque Control (DTC) andits future development firstly. By analyzing a type of DTC method based onsynthesized vectors, a improved DTC method fed by three-level inverters wasgiven. Through the simulation in MATLAB/ Simulink, the correctness andfeasibility of the given control scheme was verified.(5) Finally, it introduced the future work and development.
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