Research On Analysis And Detection Of Islanding Operation Characteristics Of Microgrid

Microgrid can solve the problem of large-scale grid connection of distributed generation and improve the reliability of distribution network.In order to avoid unplanned islanding operation,or to realize seamless switching between grid connected and islanding modes,microgrid requires high speed and reliability of islanding detection.Combined with the diversity of load characteristics and the flexibility of distributed generation control strategy,the islanding operation characteristics and islanding detection methods of distributed generation system are studied.The islanding performance of microgrid is the basis of islanding detection.Firstly,the possibility and harmfulness of islanding are analyzed,and the necessity and importance of islanding detection are discussed.Secondly,based on the detection mechanism,the power change characteristics of islanding operation are described,three kinds of simulation models are established,and the difference of voltage change between islanding and other non islanding events is introduced.In addition,different islanding detection methods based on differential eigenvalues are simulated,and their advantages and disadvantages are analyzed.At last,two islanding detection methods based on differential eigenvalues are proposed to detect islanding phenomenon.According to the characteristics of power system load variety and time-varying,an island detection method based on resistance variation is proposed.In this method,the derivative of the equivalent resistance to the frequency is taken as the islanding detection index,and combined with the dynamic threshold,the islanding detection of micro grid with inverter type DG and synchronous type DG can be carried out quickly and accurately.The simulation results under islanding and various non islanding events show that this method can accurately detect islanding events in microgrid with different types of loads,and is not affected by non islanding events such as short circuit and load switching.Based on the analysis of the change of power flow in microgrid,an island detection method based on the change of reactive power is proposed.This method combines the relationship between the frequency deviation at the common connection point and the reactive power before and after the islanding,and takes the variance of the reactive power change rate as the detection index to identify the islanding.The simulation results show that the method is fast and simple compared with other passive islanding detection.This method will not cause any interference to the system,and can be applied to a variety of distributed generation systems,and avoid false tripping in various non-islanding events.