Research On Fault Monitoring Technology Of DC Distribution Network

The emergence of flexible DC distribution technology solves the contradiction between the increasing load demand and the transmission capacity limitation of traditional AC power grid,and injects new vitality into the development of distribution network.Flexible DC distribution network has obvious advantages in facilitating the access of distributed generation and energy storage equipment,improving power supply quality,increasing power supply radius,reducing line cost,etc.,which is widely concerned by scholars at home and abroad,and is an important development direction of urban distribution network in the future.In view of the analysis of the existing DC domain topology,combined with the comparison of the advantages and disadvantages of three kinds of topology in the future DC distribution system,as well as the discussion of the principle and preliminary assumption of the voltage level of DC distribution system,the two terminal power supply topology is selected as the basic topology of the DC distribution system modeling in this paper,and the DC voltage level is selected as± 10 k V。 In the design of the converter,the constant DC voltage reactive power control strategy and the constant active reactive power control strategy are selected to control the AC / DC converter based on two-level voltage source;The electromagnetic transient simulation model of DC distribution system is established in PSCAD / EMTDC environment.According to the transient characteristics of line to ground capacitive current when DC distribution network is in fault,a fault area judgment method based on DDL algorithm is proposed.The method uses DDL algorithm to determine the fault area.Through a large number of simulations,it is verified that the method is not affected by fault location,fault type,transition resistance and fault distance.At the same time,this paper introduces the basic requirements of protection partition and fault area judgment of DC distribution network system,and analyzes the fault modulus,which lays a foundation for fault area judgment and fault location.Aiming at the problem that the current general fault location method uses the total electric quantity at both ends of the line to locate the fault,which leads to the insufficient positioning accuracy,this paper proposes a fault location method based on the fault area judgment and using the electric quantity at both ends of the fault area to locate the fault in the obtained fault area.According to the relationship between the electrical quantities at both ends of the fault area,the distance of the fault point is calculated.According to the least square fitting,the electric quantity is derived,and the final fault distance is calculated according to the genetic algorithm.The location accuracy of this method meets the requirements of engineering application,and the fault type and the fault distance will not affect it.The proposed ranging method’s is verified by comparative experiments.