The Control Strategy Research Of Photovoltaic Systems

Nowadays, the growing energy demands bring the two problems of environmental pollution andenergy crisis in each country. New energy technologies and energy-saving technologies have becomea major area of growth in global energy investment, especially clean and non-polluting solarphotovoltaic power generation technology. However, the cost of photovoltaic power generation is stillrelatively high and the conversion efficiency is low. The control strategy for PV system has importantimplications for promoting solar development and application.This thesis makes a widespread thorough research on the control strategy for PV systems. Themain contents are listed as follows:Firstly, the equivalent circuit has also been researched basing on the principle of photovoltaicarray, and the mathematical models and MATLAB simulation models of photovoltaic array areestablished under the equivalent circuit,and then the output characteristics of photovoltaic array hasbeen analyzed on the basis of simulation model. The article gives four different types of simulationmodel for PV cells, which do great help to design system simulation under different circumstance.Secondly, the principle of MPPT has been introduced, then serval improved methods wasproposed after analyzing several common MPPT algorithms. Several simulation models for PVsystem are developed with MATLAB and hardware vertificicatuion circuit is built, then the improvedalgorithms have been verified on the simulation platform.Thirdly, a coordinated charging control strategy has put forward based on traditional charingmethod, after analyzing battery charging characteristics and charging methods. It makes sure that thephotovoltaic arrays and lead-acid batteries work in their best condition when the lead-acid batteriesare in proper charging characteristics. So the lead-acid batteries can store more energy and theconversion efficiency of photovoltaic power generation system is improved.Finally, the grid-connected PV systems have been presented, and double-stage grid-connectedPV system simulation models are established, then improved Increment Conductance（INC）methodwith variable step-size and P&O method have been implemented on the two PV grid-connectedsimulation models, and the result of simulation showed that the variable step INC algorithm couldimprove tracking efficiency well.