Research On Multi-inverter Islanding Detection In Distributed Generation

As the distributed generation with renewable energy has a higher pervasiveness,high-capacity distributed generation is paid more attention to the power supply technology of the power grid.Multi-inverter can realize redundant power supply and large-capacity power supply in parallel,which improves the system's reliability and flexibility,is the current trend of distributed power grid.At present,most of the research on islanding detection focuses on the single-inverter grid-connected detection.Due to the dilution effect and other issues,the islanding detection becomes more complicated.Therefore,the multi-inverter islanding detection in distributed generation for the grid is essential for efficient and stable operation,is an important issue to be solved.Firstly,this paper studies the structure of PV grid-connected system,establishes a model of PV grid-connected,and discusses the key technology of maximum power point tracking,inverter control methods and so on.The selection of control methods for grid-connected operation and islanding operation with multi-inverter parallel connection is studied.The problem of circulating current with multi-inverter parallel connection is analyzed,and the basic framework of parallel inverters is constructed.Then the commonly used islanding detection methods are systematically summarized and compared,focusing on the analysis of over/under voltage and over/under frequency method,active frequency dirft method,slip-mode frequency drift method and active frequency drift with positive feedback method,Through the description of non-detection zones by these methods,the distribution of dead zones under different parameters and the possible reasons for failure detection are given,providing theoretical guidance for further research.Secondly,through the analysis of each detection method under the conditions of multi-inverter parallel connection,the principle of the dilution effect is explained,and the parameters selection and optimization in the active frequency drift with positive feedback method are calculated and analyzed in detail.adaptive islanding detection method is presented under the condition of parallel multi-inverter:through the positive feedback coefficient k adaptive value,under the conditions of load conditions change so that the power quality and detection results at the same time meet the requirements of the inverter;through The initial value of the chopper factor cf₀ adaptive method to solve the error caused by the inverter dilution effect.Finally,the simulation model is set up by the software,in the process of simulation not only simulate inverter under different load state of the island,but also load mutation state and grid voltage state.The results show that the new method can accurately identify the island state and non-island state,and take protective measures,and the method has less impact on the power quality.In addition,the islanding detection experiment of the grid connected inverter is carried out on the intelligent micro grid platform of Hebei University of Technology to verify the effectiveness of the islanding detection method.