Research Of Three-level Asynchronous Motor DTC System Based On Fixed Synthesizing Vectors

Multi-level inverter technology has become a key study object in high voltage and high power variable frequency speed regulating field. As described in many literatures, using multi-level technology, the voltage stress on switches can be reduced, the shape of output waveform can be improved and the rate of voltage can be increased. Diode-clamped three-level inverter is the most investigated topology at present. Direct Torque Control (DTC) is an advanced induction motor control technology has been widely researched and applied for the characteristics of briefness, robustness, excellent dynamic response. So this paper focuses on the study of direct torque control of induction motor based on diode-clamped three-level inverter.In this paper, the mathematical model of three-level inverter and induction motor are set up firstly. The relationship of diode-clamped three-level inverter between neutral point potential fluctuation and output current is achieved. The paper introduces the principle of direct torque control and the latest development strategy. Several problems of three-level inverter should be solved are analyzed. Finally a DTC method based on synthesized vectors of three-level inverter is researched. Through the simulation in MATLAB, the correctness and feasibility of the improved control scheme are verified.Speed close-loop is a necessary part in three-level inverter variable frequency speed regulating DTC system. Speed sensor-less technology is a develop trend. Applying the high performance flux observer, two kinds speed estimation algorithms are designed. Simulation results show the feasible of the method.