Three-level Inverter Induction Motor Direct Torque Control

Multi-level inverter can be used in high-voltage and high-power variable-frequencyspeed regulation fields, because it has significant advantages, such as low voltagestress on switches, less distorted output and so on. As one kind of advanced controlstrategies, Direct torque control(DTC) has been widely researched. But most of thework concentrates on two-level inverter. Thus, it is necessary to research DTC fed bymulti-level inverter.Using TMS320LF2407 as control-core, this paper design a suit of DTC controlsystem based on three-level neutral point clamped (NPC) inverter, and has done sometheoretic research as well as experimental analysis.Firstly, through consulting all kinds of reference, this paper summarized thedevelopment of the direct torque control (DTC) and the Multi-level inverter, andmade the significance of reaching on DTC based on three-level NPC inverter. Theproblems existing in the system are studied.Secondly, the mathematical models of induction motors had been analyzed,meanwhile, this paper summarized the DTC taking traditional two level inverter asthe example.Thirdly, the principle of three-level NPC inverter had been analyzed, and then theuniversal mathematical models of the control system are set up. The several DTCstrategies based on three-level inverters were introduced. By analyzing thesynthesized vectors method, a improved DTC method was given. Simulation of thecontrol system using MATLAB and a series of qualitative analysis were conducted.Fourthly, this paper designed the DTC system of induction motor fed by three-levelinverter. In this chapter, the hardware and software design were all lised clearly.Finally, experiments have been done on this practical system. Some experimentalresults were got and were analyzed.