Research On The New Composite Method Of Isolated Island Detection Of Photovoltaic Grid-Connected System

With the rapid development of the global economy,the worldwide use and demand for energy has increased rapidly.However,traditional energy sources such as fossil natural gas have been depleted.It has brought many environmental problems and has become a major problem facing all countries in the world.Vigorously developing clean alternatives is the trend of the times,and solar energy,a relatively more abundant and efficient green new energy source,has received attention and wide recognition,and has gradually occupied an important position of new energy.The large amount of new energy entering the distribution network will trigger A series of questions.One of them is the island effect.The islanding effect poses a serious threat to the safe operation of maintenance personnel and electrical equipment.Therefore,it is urgent to ask the relevant departments to conduct island inspection of the photovoltaic power generation system.This paper first studies the mechanism of island effect,various methods and classification of island effect detection,discusses how to detect island effect and current detection standards,and analyzes the conventional circuit of island effect detection and its application range.Secondly,several components such as photovoltaic array and inverter are studied,and the basic model of photovoltaic power generation system is established.The variation of voltage and frequency when active power and reactive power are not balanced without taking any measures is deduced and verified by simulation.Then the mathematical modeling and simulation verification are carried out for the active frequency shift detection method and the active frequency shift detection method with positive feedback.The effects of initial chopper factor and feedback rate on the island detection system are analyzed.Aiming at the problems of slow detection time,large blind area and inaccuracy of traditional island detection strategy,a composite island detection method of passive detection and active frequency shift method with power conversion rate perturbation combination is proposed.In addition,a simulation model of island detection was built under MATLAB/Simulink environment to study various performance of island detection under different loads,analyze the phenomenon of blind area of island effect,and compare it with over/under voltage method and active frequency shift method.Simulation experiments show that the method presented in this paper can accurately detect the occurrence of isolated island effect in a short time under various load conditions and has better accuracy and advantages.Finally,for the problem of island detection in parallel operation of multiple inverters,three combination methods with characteristic significance are selected:one adopts the passive island detection method,the other adopts the active frequency shift method,both of them use positive feedback active frequency shift method;and both of them use the new composite island detection method for experimental analysis.It is proved that the method is still applicable to multi inverter,and the detection effect is superior.