Study On Distribution Network Fault Characteristics Considering The Influence Of Photovoltaic Access Capacity

With the increasing access capacity of Distributed Generation(DG),distribution network is facing great challenges in operation security and power supply stability.After DG is connected to the distribution network,the system is transformed from the original simple single power supply network to the complex multi-power supply network.When short circuit fault occurs,the direction of current is difficult to determine,and DG is connected to the distribution network under various conditions such as different capacity,quantity,location and type.Therefore,the original protection scheme applicable to traditional distribution network cannot meet the protection requirements of distribution network with DG access.In view of the above problems,the main research work of this paper is as follows:Based on the external characteristics of photovoltaic cells,the DG equivalent circuit mathematical model was established to analyze the voltammetry characteristics and power-voltage output characteristics,and the maximum power point tracking was realized by disturbance observation method.Then,focusing on three-phase inverter module,outer loop control module and inner loop control module,the grid-connected control process of DG in normal operation is discussed.Finally,the control mode of DG in distribution network failure is analyzed.For the dual feeder distribution network with single DG access,the influence of current protection on the feeder terminal bus,non-terminal bus and first bus of distribution network is analyzed when the fault occurs in different sections of the line.On this basis,the influence of short circuit faults at different access capacities and different locations on current protection of distribution network is analyzed by taking two DG connections as examples.Finally,a simulation model is established on PSCAD to divide fault locations into upstream,downstream and adjacent lines of DG access point,and verify the accuracy of theoretical analysis on the influence of different access locations and capacities of DG on current protection of distribution network when faults occur in different areas of distribution network.Aiming at the existing adaptive current current disconnection protection method applicable to traditional distribution network without DG access,the shortcomings and existing problems of using the existing method to set the action current after DG access are analyzed,and an improved adaptive current disconnection protection method considering multiple DG access is proposed.The method can adjust the setting value of protection action current in real time according to different short-circuit fault locations and fault types.Finally,a simulation model is established through PSCAD to verify the effectiveness of the proposed setting method.