Research On Improved Performance Of Direct Torque Control Of Voltage Source Three-level Inverter

In recent years,high-power multi-level inverters have gained more and more attention in the field of industrial production.Compared with the two level inverter,the output of the three-level inverter has the merits of higher power quality,lower harmonic content,better electromagnetic compatibility and lower switching losses.Therefore,it has been widely applied in the medium and high voltage and high power AC motor variable speed field.The direct torque control system has fast torque response and no overshoot.And it is an AC speed regulating method with high dynamic performance,but it still exists some shortcomings.The direct torque control system of the inverter is taken as the research object which is optimized by using the fuzzy logic control.The related theory,methods and key technologies are researched in-depth.The main work is as follows.Firstly,this paper starts from the basic topology,basic principle and control method of the three-level inverter,and emphatically analyzes the modulation process of the three-level inverter by space vector modulation algorithm,and deduces the 27 kinds of switch combinations and corresponding duty cycle time.The basic principle of direct torque control and the dynamic mathematical model of both asynchronous motor and permanent magnet synchronous motor are analyzed in detail.Then,using the MATLAB/Simulink simulation software to build a three-level inverter driven asynchronous motor voltage SVM-DTC system.Secondly,the paper systematically introduces the basic principle and control method of fuzzy logic control,and the PI type fuzzy logic controller which is applied to the voltage source three-level inverter driven asynchronous motor SVM-DTC system.The feasibility,correctness and reliability of the control strategy are verified by simulation experiments.Finally,based on the advantages of voltage source three-level inverter SVM-DTC AC speed regulation system and combining the fuzzylogic controller,both are integrated into the marine electric propulsion system.The SVM-DTC simulation model of ship based on permanent magnet synchronous motor is built.The PI fuzzy logic speed controller is applied to this system,and the simulation experiments of these two schemes are carried out.Then,the relevant waveforms are compared and analyzed.The simulation results show that the latter is more superior in suppressing the current harmonics and improving the system response.