Fault Handling Method In DC Distribution System Based On Dispersed Capacitor And Fault Zone Partitioning Strategy

With the development of distributed power generation,dc energy storages and the wide application of dc loads,dc power distribution technology is getting more and more attentions for its flexible power transmission,low conversion loss and large transmission capacity.When a dc short-circuit fault occurs,line current increses rapidly.If the fault cannot be interrupted and isolated in time,the whole system may suffer from undervoltage and it may cause damage to converters.It may even lead to total blackout throughout the system.The developing speed of dc fault is in millisecond level,demanding fast actions for the fault detecting and locating,fault current blocking,fault point isolating and system recovery.The fault handling technology in dc distribution system is the focus of this research.Firstly,the applicability of different types of converters in dc distribution system is studied.Based on the analyses of dc fault characteristics,the overall technical requirements for fault handling in dc distribution system are proposed.Secondly,to solve the voltage collapse problem during the fault handling progress,the head-end-dispersed capacitor scheme is proposed.By dispersing voltatge-stabilizing capacitors on the dc outlet of converters,the system-wide voltage collase and overcurrent is suppressed.The transient features during sudden power changes and faults are analyzed,according to which the capacitor parameters are designed.The protection critiria setting and the relative position of dc breakers are discussed.Lastly,to solve the power interruption problem in healthy networks,the diode-based automatic fault zone patitioning method and fault locating method are proposed,using the converters with fault self-cleaning capability.By the uniconductivity of the power diodes,dc distribution system is devided into several zones once the fault occurs,which reduces the area of incluence of the fault.According to the unique fault characteristics under the proposed scheme,the integrated protection scheme is proposed,as well as the overcurrent critirum and fault locating method.The technical adaptivity of the diode-based fault zone patitioning scheme is then analyzed.By applying the proposed dispersed capacitors and diode-based zone patitioning method,the influence of the fault is reduced and the recovery after the fault is faster,and the fault ride-through capability of the healthy area is enhanced.Theoretical analyses and simulation results verify the effectiveness and accuracy of the proposed methods.