DC Fault Current Calculation and Fault Level Analysis in MMC-MVDC System

The broader use of modular multilevel converters (MMCs) in medium-voltage direct current (MVDC) systems combined with the multiple possible network topologies of a multiterminal dc (MTDC) network pose major challenges to fault analysis, short-circuit calculations and, eventually, system reliability. In order to evaluate dc fault levels in MTDC systems with MMCs, this paper derives an expanded RLC equivalent model for representing converters and networks with system characteristic matrices, based on which, state-space analysis can be implemented to facilitate fault current calculations. Analytical calculations and simulation results of MMC and MTDC branch currents across multiple scenarios and different configurations of an MTDC network with five converters identify fault influencing factors and reveal unique characteristics of fault analysis in MVDC systems.