A reliability analysis method of HVDC relay protection based on MDD-GO methodology

Aiming at the state explosion problem caused by complex connections of the components and the computational explosion one caused by shared signals in the reliability analysis of HVDC relay protection using goal oriented (GO) methodology, this paper proposes a reliability analysis method combining Multivalued Decision Diagram (MDD) with GO methodology for HVDC relay protection. Firstly, the mapping rules from GO operators to MDD are analyzed and the MDD model of HVDC relay protection is established by converting GO diagram to MDD. Secondly, the multivalued function expression is used to reflect the relationship between component state and system state, the merger principles of path sets leading to relay protection misoperation and cut sets leading to relay protection refusal action are studied, and the method obtaining the minimal path sets and the minimal cut sets is proposed. Thirdly, the occurrence probability of the multivalued function is calculated according to Shannon decomposition recursive formula, and the state probabilities of HVDC relay protection are calculated by the occurrence probability formula and annual statistics of each protection component. Finally, the importance rate of each minimal path set leading to misoperation and minimal cut set leading to refusal action is analyzed, so the main influencing factors are found out. The correctness of the proposed reliability analysis method based on MDD-GO methodology is verified by the whole set of HVDC line protection. The proposed MDD-GO methodology solves the computational explosion problem by using n-variable discrete multivalued function expression and the state explosion problem by searching the path sets and cut sets directly through MDD model instead of listing the complex state combinations of GO operators. And the importance rate of each minimal path set and minimal cut set is convenient to pay attention to the main module of HVDC line relay protection and improve the reliability of the overall relay protection.