Research On Control Strategy Of Modular Combined Converter In Photovoltaic DC Concentration System

Solar energy is being vigorously developed as a renewable clean energy.The various problems of traditional AC collection and grid connection technologies:power quality harmonics,low system stability,and excessive line losses are gradually highlighted.As a new photovoltaic power station collection solution,photovoltaic DC collection technology has certain advantages in economy,energy utilization rate and system power generation efficiency.However,there are still various technical problems that need to be solved in the application research of photovoltaic DC collection technology at this stage.This article has conducted a series of discussions and studies on the technical problems of the DC boost structure in the photovoltaic DC collection system:The paper first determines the specific structure of the DC converter in the photovoltaic DC collection system:a combination converter with input parallel output and series connection;In the functional DC/DC converter,the single-module topology of the cascaded IPOS-DC/DC,DC boost structure is selected,and the specific parameters of the topology are designed.The simulation verifies the stability and feasibility of the single-module topology.Secondly,the paper analyzes the various factors that affect the voltage balance and researches on the problems that the serial output terminal often fails to normalize the voltage when the IPOS-DC/DC boost structure is often applied in the photovoltaic DC collection system,which affects the normal operation of the system.An improved drooping voltage equalization control strategy suitable for the structure is implemented.The preliminary voltage-sharing control is realized by using the submodule circuit inductor current compensation value and the droop characteristics of the serial output terminal voltage.In the face of the droop control method,the static difference and For accuracy problems,the droop control is improved once again to achieve a better pressure equalization effect.The stability and rationality of the system are analyzed through smallsignal modeling.Matlab/Simulink simulation verifies the feasibility and pressure equalization effect of the strategy.Finally,the paper builds a 4-module 2MW photovoltaic DC collection two-level structure in the Matlab/Simulink simulation platform,analyzes and discusses the maximum power tracking characteristics of each module under ideal environment and light intensity changes,and studies a sub-module that implements MPPT The phase-shift modulation technology basically maximizes the independent output power of each module;further analyzes the hot-swap problem of the cascade structure to achieve a balanced output power of each module.