The Research On Control Strategies Of Three-level Inverter

As the most widely used multi-level inverter circuit,three-level inverter, compared with two-level inverter, has the advantage of low harmonic in output and low switching power loss. For its excellent performance, three-level inverter has replaced the traditional two-level inverter and became one of the main methods of speed modulation of large capacity high voltage motor. Therefore, it’s of great significance to make a research of three-level inverter.The thesis tightly surrounds the Neutral-Point-Clamped three-level inverter, make a deeply research of its main circuit and the working principle, and establishes the mathematical model of three-level inverter.The thesis make a detailed analysis of the basic principles and concrete steps of SPWM and SVPWM for the Neutral-Point-Clamped three levels inverter. For SPWM, the thesis make a detailed comparison of several different methods, such as carriers in same phase、carriers in reverse phase、carriers longitudinal displacement、zero-sequence component inject、third harmonic inject, and make out a analyzation of the output characteristics through the Fourier transform. For SVPWM, there are two methods, six small sectors and four small sectors. The thesis also make a comparison between the two methods of its output characteristics. The thesis also uses basic topological structure of diode-clamped three-level inverter as basic, analyses the reason of lopsided neutral-point voltage, and gives the modulated algorithm of neutral-point electronic charge. Then there are several simulation models of various modulation schemes established by Matlab/simulink. Through making FFT analysis of every modulation schemes, the thesis demonstrate the effectiveness of the modulation schemes and make a comparative analysis of the DC voltage utilization、harmonic content and other output characteristics.At last, the thesis tightly surrounds the vector control widely used in locomotive traction. There is a detailed analysis of the principle and implement process of the motor speed control system using the magnetic field orientedvector control based on SVPWM. The simulation of traction inverter is built in the matlab/simulink. To virify the property of rapid response, the thesis makes simulations of the motor starting and braking. Moreover, theses simulations also verify the motor traction characteristic and the effectiveness of control methods of this thesis.