| The shortage of energy sources has led to the development of new energy sources,and it causes a series of problems due to a large number of new energy sources connected to the power grid,one of which is the islanding effect.Islanding operation will cause a serious threat to the safety operation of the maintenance personnel and equipment,so it is necessary to detect the islanding in the new energy power generation system.At present,the research on the islanding detection technology has become mature,domestic and foreign scholars put forward a variety of islanding detection scheme,such as active frequency shift method,the specific harmonic injection method,and so on.However,it is difficult to guarantee the low disturbance to the power grid while the detection method is fast and accurate.At the same time,due to the increasing of new energy capacity,some of the islanding detection methods have been unable to meet the requirements.Therefore,it is necessary to find a good way to solve these problems.In this thesis,we study the control strategy of grid connected inverter,and establish mathematical models of the three kinds of active frequency shift methods and finish their simulations.At the same time,we analysis the influence factors of active frequency shift performance and give the improved detection method.At the same time,it is inevitable that the islanding detection methods based on active frequency shift will cause disturbance to the power grid,so this thesis focuses on the detection method of reactive power disturbance,and analysis of its working principle.Based on the previous studies,the relationship between new energy capacity and load capacity is established and we make a quantitative analysis of the reactive power disturbance,and has carried on the simulation,the simulation results show that the islanding detection method based on reactive power disturbance can not only satisfy the speed and accuracy at the same time,but also reduce the disturbance of power grid. |
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