Reserch On Control Strategy Of Three-level Grid-conneced Photovaltaic Inverter

Along with the increasing efforts of the government to support the photovoltaic, new energy is booming, and its generation capacity is increasing. Medium and large-scale photovoltaic projects connected the grid become more and more. Large-scale photovoltaic(PV) grid projects are constructed increasingly, the demand of grid-connected inverter is becoming bigger and bigger. In the field of grid-connected inverters, three level inverter is more suitable for its large capacity, small harmonic content and high conversion efficiency, which aroses extensive attentions of many scholars, This paper study three-phase three-level NPC PV grid-connected inverter to output high-quality electric energy.This paper propose an improved algorithm of the grid control about three level inverter inherent problems: common mode voltage suppression problem and neutral voltage offset based on LCL filter.Firstly, this paper establishes the mathematical models of the inverter, introduces a SVPWM of the three-level inverter, and analyzes the grid inverter output for the following analysis and network control to lay the foundation; Secondly, this paper introduces three-level three-phase grid inverter dual-loop control method, it gives the parameter design of the inner loop and outer loop. Thirdly, this paper analyzes the inherent problems of three level inverter: common mode voltage suppression and neutral voltage balance issue, and puts forward a kind of method based on the superposition and substitution of auxiliary vector; Finally, the paper establish the simulation model to verify this method of the paper, the simulation control effect is good, photovoltaic grid-connected integrated simulation system has been verified.