Study On The Fault Self-Recovery Strategy In Two-Terminal DC Distribution Network

DC Distribution Network(DCDN),which is considered to have several advantages such as lager power supply radius and capacity,higher power quality,and more convenient for distributed sources plugging in,is one of the most important direction in distribution grid research field.Some key technologies of DCDN received broad attention worldwide,such as voltage rank sequence,network topology,operating control strategy,and protection method.Rapid fault self-recovery technology plays a crucial role to promote power supply reliability of DCDN by detecting,locating and clearing fault accurately and rebuilding system voltage rapidly.At present,researches of rapid fault self-recovery technology of DCDN are mainly focus on pole-to-pole fault protection method.Research on pole-to-ground fault locating method and recovery strategy of unipolar and bipolar fault is still in early stage.For the above,this paper researches on fault section locating,isolating and recovering.Main works and results are showed below.1)Based on a two terminals Modular Multilevel Converter based DC Distribution Network(MMC-DCDN),common network topologies of DCDN,main connection schemes of converter station and the operation principles of MMC are illustrated.inside structure and performance parameter of different DC Circuit Breakers(DCCB)and its install topology in DCDN are introduced respectively.2)Characters of pole-to-ground fault of DC side high-resistance-grounded pseudo bipolar system are analyzed in detail,a rapid fault section locating method of pole-to-ground fault based on wavelet transform module maximum of fault current traveling wave.Pole-to-ground fault recovery sequence of two different DCCB installing topologies are presented respectively based on accurate fault section locating method.3)For pole-to-pole fault,three stages of fault current are simply introduced.A pole-to-pole fault section locating method based on wavelet transform module maximum of fault current is presented.Pole-to-pole fault recovery sequence of two DCCB installing topologies are presented respectively.By simulating in PSCAD/EMTDC and MATLAB environment,correctness of above fault section locating methods and both feasibility and rapidity of above fault recovery sequences are verified.