When a fault occurs in a DC system,the fault current rises rapidly with no zero-crossing point which makes fault-line selection and fault-type identification difficult.In this paper,an online detection and protection ...When a fault occurs in a DC system,the fault current rises rapidly with no zero-crossing point which makes fault-line selection and fault-type identification difficult.In this paper,an online detection and protection method based on graph theory,namely the“double D method”,is proposed for fault-line selection and fault-type identification in DC systems.In the proposed method,the entire distribution network is visualized as a“map”with vertices representing the line convergence points and edges representing the connection lines.A network topology matrix“D”is formed by detecting the current directions as the current directions are altered following a fault,whereas the current directions at the ends of non-fault lines remain the same.In order to prevent misjudgment problems arising from power flow reversal,the rates of change of the fault currents are used to further determine whether a fault has occurred and the“double D method”is introduced to identify the fault type.Simulations results with different fault types verify the effectiveness and reliability of the proposed method.展开更多
A classification of pentavalent symmetric graphs of order twice a prime square is given. It is proved that such a graph is a coset graph of Z3.A6 （non-split extension）, or a bi-coset graph of an extra-special group ...A classification of pentavalent symmetric graphs of order twice a prime square is given. It is proved that such a graph is a coset graph of Z3.A6 （non-split extension）, or a bi-coset graph of an extra-special group of order 125, or the standard double cover of a specific abelian Cayley digraph of order a prime square.展开更多
Two kinds of unconnected double fan graphs with even vertices,(P^((1))_(1)∨(P^((1))_(2n)∪P^((2))_(2n)))∪P_(2n+1)∪(P_(1)^((2))∨K_(2n))and(P_(1)^((1))∨(P^((1))_(2n)∪P^((2))_(2n)))∪(P_(1)^((2))∨K_((1))^(2n))∪(P...Two kinds of unconnected double fan graphs with even vertices,(P^((1))_(1)∨(P^((1))_(2n)∪P^((2))_(2n)))∪P_(2n+1)∪(P_(1)^((2))∨K_(2n))and(P_(1)^((1))∨(P^((1))_(2n)∪P^((2))_(2n)))∪(P_(1)^((2))∨K_((1))^(2n))∪(P^((3))_(1)∨K_((2))^(2n))were presented.For natural number n∈N,n≥1,the two graphs are all graceful graphs,where P^((1))_(2n),P^((2))_(2n)are even-vertices path,P_(2n+1)is odd-vertices path,K_(2n),K^((1))_(2n),K^((2))_(2n)are the complement of graph K_(2 n),G_(1)∨G_(2)is the join graph of G_(1)and G_(2).展开更多
基金Thanks for the financial support from the following fund projects:Project Supported by National Natural Science Foundation of China(51607070)。
文摘When a fault occurs in a DC system,the fault current rises rapidly with no zero-crossing point which makes fault-line selection and fault-type identification difficult.In this paper,an online detection and protection method based on graph theory,namely the“double D method”,is proposed for fault-line selection and fault-type identification in DC systems.In the proposed method,the entire distribution network is visualized as a“map”with vertices representing the line convergence points and edges representing the connection lines.A network topology matrix“D”is formed by detecting the current directions as the current directions are altered following a fault,whereas the current directions at the ends of non-fault lines remain the same.In order to prevent misjudgment problems arising from power flow reversal,the rates of change of the fault currents are used to further determine whether a fault has occurred and the“double D method”is introduced to identify the fault type.Simulations results with different fault types verify the effectiveness and reliability of the proposed method.
基金Youth Science Foundation of Northwest University for Natjonalities(X2007-012)National Nationalities Commission Science Foundation of China(05XB07)NSFC(40301037)
文摘A classification of pentavalent symmetric graphs of order twice a prime square is given. It is proved that such a graph is a coset graph of Z3.A6 （non-split extension）, or a bi-coset graph of an extra-special group of order 125, or the standard double cover of a specific abelian Cayley digraph of order a prime square.
基金the National Natural Science Foundation of China(11702094)the Fundamental Research Funds for the Central University(3142015045)。
文摘Two kinds of unconnected double fan graphs with even vertices,(P^((1))_(1)∨(P^((1))_(2n)∪P^((2))_(2n)))∪P_(2n+1)∪(P_(1)^((2))∨K_(2n))and(P_(1)^((1))∨(P^((1))_(2n)∪P^((2))_(2n)))∪(P_(1)^((2))∨K_((1))^(2n))∪(P^((3))_(1)∨K_((2))^(2n))were presented.For natural number n∈N,n≥1,the two graphs are all graceful graphs,where P^((1))_(2n),P^((2))_(2n)are even-vertices path,P_(2n+1)is odd-vertices path,K_(2n),K^((1))_(2n),K^((2))_(2n)are the complement of graph K_(2 n),G_(1)∨G_(2)is the join graph of G_(1)and G_(2).
