Reliability modeling and evaluation of VSC-HVDC transmission systems

This paper presents an improved reliability modeling and an analytical reliability evaluation of Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) transmission systems. First, two VSC topologies, namely Modular Multilevel Converter (MMC) and Cascaded Two-level (CTL), are thoroughly studied. Then detailed reliability models of converters in different topologies are established based on the k-out-of-n model. Furthermore, a reliability assessment procedure for transmission systems is developed. The presented method has been employed into an assumed VSC-HVDC bipolar transmission system. Converters in two topologies as well as corresponding transmission systems are compared with respect to reliability. Moreover, impacts of redundant modules on converter reliability and system reliability are examined. The numerical results show that the CTL converter is more reliable but need more IGBT cells than the MMC do. When the redundancy rate increases, the reliability of a MMC-based system improves more significantly than that of a CTL-based one.