Research On MPPT Control Method For Large-Scale Marine Photovoltaic System

Recently,as people pay more and more attention to the greenhouse effect and other environmental problems,countries all over the world have adopted different policies.These policies are designed to promote and support the development and efficient utilization of all types of clean energy.In the field of shipping,it is undoubtedly important for the future to vigorously develop green shipping technology for energy conservation and emission reduction,combat the effects of climate change,and achieve the goal of Carbon Peak and Carbon Neutral.Under this background,concepts such as "green ship" and "intelligent ship" gradually emerged,and the research on large-scale marine photovoltaic(LSMPV)system has become worldwide popular.For the LSMPV system equipped with a large-scale photovoltaic(PV)array,it is prone to frequent environmental disturbance during the ship movement,resulting in severe fluctuation of output.Moreover,prolonged exposure of high temperature,high humidity,strong corrosion and other extreme maritime conditions may also lead to accelerated aging rate of PV modules and decay of operating characteristics.Therefore,the special working conditions pose great challenges to the operation control of marine PV systems.Under the background of green intelligent ships,this paper studies the optimal operation control of LSMPV system.The specific research presents as follows.Firstly,the paper describes the principle of a PV cell and the equivalent circuit model.On this basis,a simulation model of the PV array is built on MATLAB/Simulink platform.Under the conditions of uniform illumination and partial shadings,the output characteristics of the PV array and the influence on Maximum Power Point Tracking(MPPT)control are analyzed and verified.Besides,when the PV array moves with the ship,frequent environmental disturbances such as partial shading and dynamic illumination will affect the output of the PV system.From the perspective of array topology,the passive suppression method of environmental disturbances is studied,and a total-cross-tied based PV array topology for large ships is proposed.On the one hand,the array topology simulation models such as Series,Series-Parallel,Total-Cross-Tied,Bridge-Linked and Honey-Comp are built based on the MATLAB/Simulink platform.Under six typical shadings,the output of each topology structure is analyzed through simulation experiments,and the optimal topology is obtained by comparison.On the other hand,marine PV array models of different aging degrees are built,and the topology with the optimal suppression ability for asymmetric aging of PV array is verified by simulation.Furthermore,traditional MPPT methods have some problems such as inaccurate prediction and long response time when applied to LSMPV systems.To address these situations,an offline MPPT method based on environmental features and the convolutional neural network(CNN)model is proposed.Numerical simulation results show that the proposed offline method can predict the maximum power point(MPP)accurately and effectively.Finally,as for the degradation of PV module,the time-window mechanism is proposed to realize the active following of the CNN model.This mechanism includes the construction and dynamic update of MPPT sample knowledge base.In addition,the optimal length of time-window under different environmental conditions and aging rates is verified by numerical simulations.The obtained optimal length of time-window provides a reference and basis for model updating when the MPPT method is applied in different environmental conditions.