Islanding Detection Technology Research DGs

With the development of the social economy,the demand for energy in various countries is increasing,and the traditional power generation technology will lead to increasing environmental problems.Therefore,countries have begun to pay attention to energy conservation and the development of new energy,providing a lasting impetus for social development in the future.With the increase of the grid-connected capacity of distributed power sources,the utilization rate of micro-grids has increased year by year,and higher requirements have been placed on traditional grid protection.Among them,the islanding effect of microgrid is one of the main problems that limit the development of microgrid.The islanding effect refers to the failure of the main power grid or the routine maintenance,which will cause the large power grid to be in a power-off state.At this time,the distributed power generation system will be disconnected from the large power grid and operate in an independent state.The difficulty of its detection is mainly due to the fact that when the island is generated,its electrical characteristics fluctuate less,and the traditional protection equipment cannot respond,resulting in the persistence of the micro-voltage undervoltage and other states.The generation of the islanding effect will seriously threaten the personal safety of the personnel,and will also affect the protection program of the power distribution system,causing damage to the electrical equipment during the closing.From this point of view,the emergence of the islanding effect will cause great harm to the existing distributed generation system.Therefore,the distributed generation system must have island detection and protection functions.This paper starts from the problem that the traditional protection scheme existing in the microgrid application is not suitable,and combines the speciality of its own islanding effect,that is,the fault characteristics when the island is generated is very small,which is not enough to trigger the action of the protection device.A voltage positive feedback islanding detection scheme based on self-oscillation is proposed,which causes the voltage to violently oscillate after several cycles after the island is generated and reaches the amplitude of the action of the trigger protection device to complete the whole protection process.In addition,in view of the special case that the island microgrid is connected to the grid and the energy transmission of the large grid is less or no,the internal protection scheme of the microgrid is also proposed.The impedance and the direction of the power flow are compared to accurately determine and locate the fault.The effectiveness of the two schemes is verified by the simulation model,which provides an effective new idea for solving the islanding effect of the microgrid.