Research On Module Multilevel Inverter

With the rapid growth of the global economy, the demand of people for power is more and more. As the energy of fossil fuels in power generation is non-renewable and nuclear power generation can provide a lot of power, but also exist waste disposal and many other issues, under this background, the wind power began to appear and have been developed. A great deal of energy impact to the traditional transmission and distribution systems when the wind access grid, to solve the above problem, Wind power use HVDC Light has become a hot topic in power system studies.The traditional output of HVDC Light is two-level or three-level, it is difficult to meet the demand of requirements of high voltage, high power for the grid. This need to develop and select the appropriate converter wind energy in order to achieve a smooth grid. Due to existence of contradiction between switching device power handling capability and switching frequency, research scholars generally start from circuit topology and control method on the converter to achieve high and low electromagnetic interference.Starting from multilevel inverter topology, the paper put common diode-clamped inverter, and cascaded inverter as the research object, study and summarizes their topological structure and working methods, describes a modular multi-level inverter topology with redundant design, this inverter has the following characteristics:simple control method, flexible structure, greatly reduce the stress of switching devices, reduce switching losses and improve system efficiency.This paper analyzes the multi-level inverter modulation strategy, proposes an optimized a carrier phase shift PWM modulation method for modular multi-level inverter, this method combined with sub-module voltage balance control, to eliminate traditional carrier phase-shifted PWM modulation method using a large number of harmonics inverter system to ensure stability of the system.Then the paper analyzes the basic working principle of mathematical modeling of modular multi-level inverter, built a modular multi-level inverter model with PSCAD simulation software. The simulation focus on output voltage level of the number of pre-charge policy, the carrier phase shift PWM modulation, algorithm for voltage balance control, analysis performance characteristics of modular multi-level inverter. Finally, the paper designs a modular multi-level inverter cabinet model based on shortcoming of common inverter. The article analyzes the loss characteristics of a modular multi-level inverter and the simulation results. Obtained the curve of the thermal impedance of IGBT, help to select IGBT and design cooling system of modular multi-level inverter cabinet.