Research Of Grid-connected PV System Based On MMC Under Partial Shading

With the rapid development of society,the demand for energy is increasing,and the conventional non renewable resources are becoming more and more scarce.In order to solve the problem of energy shortage and environmental pollution,people began to turn their attention to the inexhaustible and pollution-free solar energy.PV is the use of solar power generation technology using the most,in the grid connected photovoltaic power plant optimization under partial shading has been a hot and difficult research in this field,and the topological structure of PV system optimization is effective way to solve the problem of.Combining the unique advantages of modular multilevel topology in distributed energy generation,this paper improves the topology and control strategy of a modular multilevel photovoltaic grid connected topology.Firstly,the physical model and output characteristic model of photovoltaic cells are analyzed,and then the mathematical model of photovoltaic array is deduced,and the reasons of PV array power mismatch under local shadow condition are analyzed.Then,the topology of bipolar power generation system is introduced,and the working principle of BOOST circuit is analyzed.Introduces the modular multilevel converter(modular Mutilevel converter,MMC)the basic structure and operation mechanism,and combined with the characteristics of both,to optimize the design of photovoltaic power generation system based on MMC,and analyzes the basic operation principle of the system.Secondly,photovoltaic system improvement to the start and stop process analysis,design the system on-off control process and the corresponding controller;the principle of photovoltaic array maximum power point tracking is analyzed,combined with the analysis of the operation characteristics of topology,design corresponding to maximum power point tracking control strategy for the the maximum power point,voltage acquisition can realize each photovoltaic component;analyzes the process of grid system,design the controller,to achieve stable operation of grid connected photovoltaic power generation system.Finally,according to the improved topology and the control strategy designed for the system,the simulation experiment is done with MATLAB/Simulink software.According to the simulation results,it is concluded that the topology of the improved PV grid connected system can operate stably under the condition of local shadow.Moreover,compared with the conventional centralized grid connected structure,the system also has the advantages of high utilization of solar energy and low harmonic content.