Research On Direct Torque Control Of Induction Motor Based On Three-Level Inverter

Clamped multilevel inverters are very suitable for high-voltage and high-power application field, because they have many advantages such as low voltage stress on switches, small harmonic content in the output voltage waveform and good control performance. So they have been widely used in the field of high voltage frequency control. Direct Torque Control(DTC) is an advanced AC drives control principle where inverter switching directly controls the motor variables:flux and torque. DTC technology has been widely researched for the characteristics of briefness, robust, excellent dynamic response. This paper focuses on the study of direct torque control of induction motor drive based on diode-clamped three-level inverters.Firstly, this paper analyses the development and the present situation of the multilevel inverters topologies, the development of AC variable speed techniques and the characteristic of DTC are discussed, and also, the purpose and significance of this research are pointed out.In this paper, the mathematical model of three-level inverters and that of induction motors have been established. Because there is some existing relationship between the diode-clamped three-level inverters and the load-induction motors that the inverters' neutral-point potential can be affected by some output currents, so building an universal model is necessary. A unified mathematical model is constructed inα-βtwo-phase stationary coordinate for further research.Latterly, this paper analyses the principles and basic structure of DTC, At the same time, three flux observation models have been established. Through analyzing the problems of three-level inverters for induction motor control, several DTC strategies based on three-level inverters are introduced. By analyzing those strategies, the fixed and improved synthesizing vectors for DTC control method fed by three-level inverters are proposed.In the above theoretical analysis, MATLAB/Simulink is used to do simulation research on the new method proposed in this paper. The simulation results show that the strategies is correct in principle.