Reliability evaluation and sensitivity analysis to UHVDC-HC considering preventive maintenance and inverter's capacity levels

Preventive maintenance (PM) improves reliability of the ultra high-voltage dc (UHVDC) line, but introduces new states, and adds the difficulty of finding the reliability parameters of the component with the PM. The hierarchical connection (HC) of the inverter improves flexibility of UHVDC, but the state spaces of the inverter and UHVDC-HC are decided by the capacity distribution between the high terminal (HT) and low terminal (LT), which has not been studied yet. In this paper, reliability of UHVDC-HC with the PM is studied. The originalities are, (1) With the impact of PM described by a nonlinear coefficient, the state space of component with PM is aggregated. It has the same size as that without PM. The only difference is the transition rate. (2) Considering power distribution between the HT/LT and its dependence on the state of the rectifier, new capacity levels of HT/LT, e.g. 75%/2, 50%/3, are defined. (3) With the capacity levels of the HT/LT differentiated, 2 existing reliability indices are extended, and 2 are newly defined. (4) A sensitivity model of the reliability of the UHVDC-HC to its parameters and the PM period is proposed.