Application Research Of Multi-Module Multi-Level Converter In Large-Scale Photovoltatic Power Station

Solar energy has attracted worldwide attention in recent years because of its great potential for development.Photovoltaic power generation because of sustainable,pollution-free,rich resources and other characteristics has become the trend of development.But due to the mutual effect of the factors such as the external environment,the output characteristics of solar photovoltaic cells and a large impact on the effectiveness of the grid-connection control system,so in order to improve the efficiency of photovoltaic power generation in this paper,Modular Multilevel Converter(Modular Multilevel Converter,MMC)technology is introduced in the photovoltaic power generation system,mainly for maximum power point tracking algorithm is optimized to improve and control strategy of photovoltaic(PV)grid research.The main research contents of this paper are as follows:This paper first introduces the research status of grid-connected technology of photovoltaic power generation,the working principle and topology of modular multilevel converter.The basic parameter selection method of MMC is analyzed,the two most commonly used modulation methods are analyzed and studied,and the modulation method suitable for this paper is selected.The working principle of the mathematical model of solar photovoltaic cell is analyzed.A photovoltaic cell model was built on MATLAB/Simulink simulation software.By adjusting the light intensity and temperature,the effect characteristic curve of photovoltaic cells under different conditions was obtained.Then,the working principle and mathematical model of several traditional methods of Maximum Point Tracking(MPPT)are introduced.Combining the advantages of the fixed voltage algorithm and the variable step size perturbation observation algorithm,an improved compound control algorithm was proposed,and the simulation model was built on the Simulink simulation software to realize the rapid and accurate tracking of the maximum power(MPP)point and complete the improvement and optimization of the photovoltaic power generation system.At last,a grid-connected control structure based on MMC with 11 level is proposed,the basic operating principle of the grid-connected control system is introduced,and the capacitor voltage equalization control strategy of MMC sub-module is deeply studied.In photovoltaic(PV)grid control is improved based on MMC optimization,the double closed loop control method is proposed to introduce a kind of PI and PR compound gridconnection control strategy of combining,built the simulation model in Simulink simulation software,the simulation experimental results show that the composite grid control strategy,applied to a photovoltaic(PV)grid system based on MMC can run normally,but also can greatly improve the power quality,verify the feasibility and effectiveness of the method.