Research On Control Methods In Photovoltaic Grid-connected System Based On Z-source Inverter

Because the fossil fuels are non-renewable and the problem of environmental pollution,the development and utilization of new energy has been imminent. The development andutilization of solar energy is an important development direction of new energy in the future,and photovoltaic power generation has become the main way in many ways, photovoltaic gridpower generation technology is an important part in photovoltaic power generationtechnology.The solar energy is the focus of energy development in the future, and photovoltaicpower generation is the trend of the development of the solar energy application, Photovoltaicgrid power generation has become an important aspect in the field of new energydevelopment.Inverter is the core part of the grid generation system, and it plays an important role inthe process of energy conversion and transmission. Because Z source inverter can overcomethe shortcomings of traditional inverter so that the inverter performance such as the safety andreliability can improve obviously, the photovoltaic grid power generation system in this paper,uses the Z source inverter instead of traditional voltage source inverter to convert electricityfrom dc to ac.At first, this paper analyzes the limitations of traditional inverter in practical applications,then emphatically introduces the special topology and working principle of Z source inverterand several kinds of modulation strategy which are suitable for the Z source inverter,highlights superiority of Z source inverter in photovoltaic application technology.Considering the uniqueness of Z source inverter topology, model Z source network andthe inverter bridge respectively, and obtain the mathematical model of three-phase Z-sourcegrid inverter system under the dq coordinate system using the link between Z source networkand the inverter bridge. In order to realize the closed loop control of the output variable, thewhole control system of three-phase Z-source grid inverter system is divided into three closedloop: grid current loop, Z-source capacitor voltage loop and shoot-through vector loop.Gridcurrent loop realizes the real-time tracking of inverter side output current and grid voltagemaking the factor of grid electricity power equal to1. Z source network capacitance voltageloop adjusts the dc bus voltage indirectly through the capacitor voltage closed loop. In orderto realize the maximization of pv array output power, shoot-through vector loop regulates theoutput voltage of pv arrays making it work in the maximum working voltage by controllingthe shoot-through zero vector duty ratios in the Z source inverter.Simulation model of three-phase photovoltaic grid power generation system isestablished by the MATLAB Simulink in this article. The analysis of simulation results suchas the photovoltaic array output waveform, capacitance voltage waveform and grid-connected current waveform proved the correctness of the established mathematical model and thefeasibility of control strategy.