Research On Fault Characteristics And Protection Technology Of DC Distribution Network

With the vigorous development of renewable energy sources(such as wind and solar energy)and the large-scale application of DC loads(such as electric vehicles and household appliances),DC distribution networks are more suitable for the development of future smart grids.Applying high-performance DC line protection methods to DC distribution networks is crucial.As the fault process of DC distribution networks is very complicated,protection technologies are difficult to apply.This article will study the fault information characteristics and protection technologies of DC distribution networks from two aspects: theoretical derivation analysis and modeling simulation analysis.Firstly,starting from the perspective of DC distribution network system design,the advantages and disadvantages of different topology structures and wiring and grounding methods of DC distribution networks are analyzed.This article studied the topology and control strategies of voltage source converter(VSC),and established a simulation model for DC power distribution networks,providing the foundation for fault characteristic analysis.Secondly,improve the longitudinal protection technology,analyze the directional characteristics of the line current within and outside the fault,solve the longitudinal protection in the distal high resistance fault within the protection may not act,and propose a longitudinal protection based on the directional characteristics of the sudden change in current.Based on the fault characteristics that can be used for protection principle,later sections will detail the research on line protection technology and fault distance measurement technology.Thirdly,the longitudinal protection technology is improved,and the directional characteristics of the line current inside and outside the fault time zone are analyzed,and the problem that the longitudinal protection may not operate in the remote high-impedance fault in the fault time zone is solved,and a longitudinal protection based on the direction of current mutation is proposed.The fault criterion and protection process are given,and the impact of various factors on protection is analyzed.Simulation results show that this method has strong tolerance to excessive resistance and noise,is not affected by distributed capacitor current,does not have strict requirements for data synchronization,and the protection action time can be stable within 1ms,meeting the requirements of DC distribution networks for protection speed and selectivity.Finally,in order to accurately locate the fault point after protection action,complementary to the above-mentioned protection technology functions,this paper analyzes the time-domain information of each stage of the fault based on the existing fault distance measurement technology,and uses the proportional relationship between the voltage of current-limiting reactors and the derivative of fault currents to solve the problem that the traditional R-L model algorithm has large differential variable acquisition errors and insufficient numerical stability when applied to DC distribution networks.A fault distance measurement technology based on the current-limiting reactor R-L model is proposed.According to the simulation results,this method exhibits good resistance to high levels of resistance and noise,requires no communication,has no strict requirements for sampling frequency,and has a fault distance measurement error within 1%,meeting the requirements of DC distribution networks for distance measurement accuracy.