Research On Current Protection For Multiple Distributed Generation Distribution Networks

The depletion of energy has led to the development of new energy sources worldwide,among which clean energy sources such as solar and wind energy have been vigorously promoted and developed internationally due to their renewability and environmental friendliness.Distributed Generation(DG)is a common way for new energy to be integrated into the large power grid.With the increasing integration of distributed generation,the network structure,power flow distribution,and operating status of traditional distribution networks have changed,and the fault characteristics of the power grid have also changed accordingly.Traditional power system fault analysis and relay protection cannot be reliably applied to multi distributed power distribution networks,and current protection schemes also need to be updated and improved to adapt to the current situation of multi DG grid connection.Therefore,this article focuses on the relay protection problem after faults occur in the case of multiple DGs connected to the grid,and conducts research on current adaptive protection based on composite sequence networks and fault phase selection methods based on current sudden variables.Firstly,this article introduces the basic concepts,grid connection methods,and control strategies of distributed power generation.Based on photovoltaic distributed power sources,the principle of PQ control was introduced in detail,and a single stage three-phase photovoltaic grid connected inverter using PQ control was analyzed.And a model was built on the simulation platform to verify the superiority of PQ control strategy and grid connection through inverters.Secondly,a simple distribution network model with a single DG connected to the grid was established,and the impact of the integration of distributed power sources on the fault current and other aspects of the distribution network under different conditions was analyzed through the superposition method during system faults.After the integration of distributed power sources,the composition of fault currents in the distribution network will become more complex,leading to the rejection and misoperation of protective devices and reducing their sensitivity.Once again,the basic principles of traditional three-stage current protection and adaptive current protection were introduced,and a typical multi DG grid connected distribution network model was established.Based on different connection situations of distributed power sources and different short-circuit types of the power grid,a composite sequence network was used to analyze the current state,and online current tuning was derived to obtain the current adaptive tuning formula,Through Matlab/Simulink simulation,it is verified that the current protection setting value after setting can vary with the system operation mode and fault type,and has the advantages of large protection range,high sensitivity,and good reliability.Finally,in order to better perform adaptive current tuning,a fault phase selection method based on current sudden variables was used according to the fault characteristics of different faults in the power grid.By using the symmetrical component method,this method greatly simplifies the process of fault phase selection and can accurately and quickly determine the type of fault.The simulation analysis of fault phase selection was conducted on the Matlab/Simulink simulation platform,verifying the superiority and effectiveness of this method.