Research On Line Protection Method Of Distribution Network With Inverter Interfaced Distributed Generation

With the development of distributed generation,more and more inverter interfaced distributed generation(IIDG)are connected to the distribution network.After the connection of distributed generation,the reliability of power supply is improved,but at the same time,it also changes the direction of power flow and the size of short-circuit current,resulting in poor adaptability of traditional protection and prone to mis-operation and refusal of operation.Considering above problems,this paper puts forward a better adaptive protection method as,main protection;The wide area protection based on centralized decision-making structure is used as the backup protection of the line to remove the fault when the main protection fails.IIDG has complex and changeable control strategy,and the output current is nonlinear.This paper analyzes the output current of IIDG under various control modes as the basis for protection setting calculation.Due to the diversity of IIDG grid connection modes and locations,the impact of IIDG access on each section of distance protection under various conditions is studied.It is concluded that when IIDG is connected to the bus,the protection section Ⅰ can act correctly,but the protection range of protection section Ⅱ will be reduced,and the reduced range is positively related to the capacity of IIDG.When IIDG isconnected to the distribution network in T-shape,the protection range of section I and section Ⅱ will be reduced.In order to improve the reliability of distance protection after IIDG access,an adaptive distance protection based on current phase difference is proposed.Through theoretical analysis,the setting calculation formulas of section I and Ⅱ of adaptive distance protection for IIDG connected to distribution network under different conditions are obtained.The value of adaptive coefficient is determined by the phase difference between the current at the protection installation and the output current of IIDG,so as to realize the adaptability of protection.Finally,a 10kV distribution network model with IIDG is established in MATLAB,and compared with the traditional distance protection,which verifies the superiority of the adaptive distance protection method proposed in this paper,and the protection range is relatively stable and less affected by the access of IIDG.Distance protection can protect the whole length of the line through the coordination of setting value and action.However,when there are many branch lines in the distribution network,the setting coordination of distance protection is more difficult;When the IIDG switching causes the change of distribution network structure,the setting value also needs to be recalculated.Therefore,this paper proposes a wide area backup protection based on centralized decisionmaking structure.The decision center partitions the distribution network according to the distribution network topology,and records the distribution network topology and zoning results in real time through the description matrix.When the distribution network structure changes,the description matrix is updated to ensure the correct action of backup protection.Finally,a 10kV distribution network model with IIDG is established in MATLAB,and the proposed wide area backup protection method is simulated and verified.The results show that the wide area backup protection can still act correctly when IIDG is switched on and off.