Research On Flexible Grounding Mode Of Distribution Network With Variable Load

With the access of distributed energy resources and the penetration of new loads,the load difference of the power grid is gradually increasing and the traditional grounding method is difficult to take into account all load characteristics.Therefore,it is necessary to consider improving the traditional grounding method to improve the security of distribution network.This paper proposes a flexible grounding technology suitable for the development of distribution networks.Its core idea is to use isolation transformers to electrically isolate the lines with large load differences in substations,so that each line can flexibly choose the appropriate grounding method according to its own line type and load characteristics.On the one hand,it can deal with the problem of neutral point change faced by the continuous development of distribution network,on the other hand,it can effectively improve the safety and reliability of distribution network.This paper mainly carried out the following work:(1)A flexible grounding method suitable for distribution network development is proposed,and its working principle is analyzed.The simulation model of a 10 k V substation is established based on MATLAB/Simulink.The characteristics of single-phase grounding fault in different grounding modes of main system and subsystem in flexible grounding mode are simulated and analyzed.The simulation results show that the isolation transformer can effectively isolate the fault,and make different outlets in the same substation work in different grounding modes,so that flexible grounding mode can be realized.The realization method of flexible grounding mode is explored,and the advantages and disadvantages of traditional isolation transformer and solid-state isolation transformer are compared and analyzed.It is considered that the solid-state isolation transformer with smaller volume has more advantages in actual transformation.(2)The working principle and topological structure of input stage,isolation stage and output stage of solid-state isolation transformer are analyzed respectively.Moreover,the mathematical model of each link is studied,the control objectives of each link are analyzed and its control strategy is designed.According to the designed control strategy,the simulation model of solid-state isolation transformer is established,and the load switching test of each simulation model is carried out,which verifies the correctness of the model.(3)The application of solid-state isolation transformer in flexible grounding mode is studied,and the simulation model of solid-state isolation transformer is applied to the substation simulation model to simulate and analyze flexible grounding mode.The feasibility of using solid-state isolation transformer to realize flexible grounding mode is verified by simulation.The simulation experiment platform of flexible grounding mode is built,and the feasibility of flexible grounding mode is further verified through the single-phase grounding fault test of different lines.In this paper,the feasibility of flexible grounding mode is fully verified by the combination of simulation and experiment,which expands the research ideas of neutral grounding mode and has certain guiding significance for the selection of grounding mode in the development of distribution network.