Effect Of DG Access To Distribution Network With Converter Interface On Protection And Countermeasure Research

In recent years,due to environmental problems,large-scale photovoltaic,wind power and other inverter-type distributed generations(IIDGs)with control strategies have been connected to the distribution network,which has become a negligible i nfluences for distribution network relay protection..In order to cope with the problems caused by the control strategy of IIDG on traditional relay protection,the mathematical model of IIDG with new grid-connected control strategy is established to analyze the impact of IIDG access distribution network on relay protection under different conditions.It is especially important to calculate the fault eigenvalue of the IIDG distribution network with control strategy and propose a solution with IIDG distribution network protection.The main tasks of this paper include:(1)The control strategy of converter-type distributed power supply in normal operation and fault condition under grid connection is studied.Considering its control strategy and low voltage ride-through characteristics,a distributed power equivalent model of inverters connected to the grid under norma l operation and fault conditions is established.(2)The analysis of IIDG is carried out on different bus lines,connected to the distribution line,distance from the fault point,capacity change,and IIDG is added and the current is not added.The effect of IIDG access on relay protection under different conditions is obtained.(3)Based on the mathematical model of IIDG normal operation and the mathematical model of segmentation control at fault time,a precise short-circuit current calculation method suitable for the new IIDG access distribution network is proposed.The algorithm can accurately obtain IIDG power distribution suitable for IIDG new grid connection requirements.Network failure characteristics.The simulation proves the correctness of the algorithm.The short-circuit current value of each branch calculated by the algorithm is compared with the short-circuit current value of the distribution network and the three-stage current setting value of each protection when the IIDG is not added,which further verifies the influence of the previous IIDG access on the protection,theoretical analysis.(4)In view of the problems that the original protection of the distribution network will be caused by IIDG access,rejection,and uncertainty of the IIDG output,a new adaptive protection for the IIDG distribution network with control strategies is proposed.The configuration of the distribution network protection scheme under the condition of IIDG access bus and IIDG "T wiring" is studied and given.Finally,the simulation verifies the correctness of the scheme.