Research On Islanding Detection Technology Of Photovoltaic Grid-connected Power Generation System

As a clean energy utilization mode,solar photovoltaic power generation can not only meet the power demand of local short-distance load,but also transfer the remaining electricity to distant areas through grid-connected mode to achieve a reasonable and effective distribution of energy.In the photovoltaic grid-connected power generation system,if the grid fails,it will easily form an island operation mode.The phenomenon of power island will endanger the safety of maintenance operators,damage the supporting equipment and related loads of the power system,and seriously affect the safe and stable operation of the grid-connected power generation system.Therefore,the problem of islanding detection must be considered in the photovoltaic grid-connected power system.This paper makes relevant analysis and research on the technology of islanding detection in photovoltaic grid-connected system.Firstly,the basic circuit principle of solar photovoltaic power generation is analyzed.Under the simulation environment,the output of photovoltaic power is simulated by building a photovoltaic panel model under the changing conditions of external illumination and temperature,and the output characteristics of photovoltaic power are analyzed by combining U-I and U-P curves.The maximum power point of photovoltaic output is tracked and controlled by grid-connected circuit model.The power output characteristics of disturbance observation method and conductance increment method are compared and analyzed.A piecewise variable step-size conductance increment optimization algorithm is proposed to reduce power loss and improve the power output efficiency of photovoltaic grid-connected system,then A photovoltaic DC array is constructed.Furthermore,the causes of islanding phenomenon in photovoltaic grid-connected system and the necessity of detection are discussed,and the basic principle of islanding detection is analyzed in detail.The passive islanding detection method and active islanding detection method are introduced respectively.At the same time,the research status and testing standards in the field of islanding detection at home and abroad are described.Several commonly used blind zone description methods are compared.Meanwhile,the single-phase photovoltaic grid-connected control system method is analyzed.By building a 3kW photovoltaic grid-connected power generation system simulation model in MATLAB/Simulink,the respective detection principles of AFD,AFDPF and SMS islanding detection methods are explained.The above-mentioned islanding detection methods are simulated and analyzed respectively.The blind area of these methods is calculated and described numerically.The main factors affecting the speed of islanding detection methods and the size of detection blind area are clarified.Based on the characteristics of voltage,current waveform and frequency variation of the parameters at the common points of grid connection,the performance of the related islanding detection methods is analyzed in terms of detection speed,detection blind area size and harmonic distortion rate,and some optimization ideas in active islanding detection methods are put forward in this paper.In order to improve the detection efficiency and shorten the detection time,the algorithm of AFDPF islanding detection is improved by superimposing frequency disturbance and introducing over/under voltage protection.At the same time,the influence of these methods on grid-connected power quality is analyzed.On the basis of active phase shift SMS islanding detection method,an SMS optimization algorithm with initial phase shift disturbance and over/under voltage protection is proposed to improve the detection efficiency reliability,and the characteristic of active phase shift and active frequency drift islanding detection algorithms is analyzed and compared.