Analytical design of a DC FCL reactor for pole-to-pole fault current in an MMC-based 2-terminal DC grid

In the case of DC grids, the fault characteristics differ from those of conventional AC system and vary depending on the converter configuration and type of fault. Additionally, for modular multilevel converter (MMC)-based DC grids, the parameters of the MMC influence the rate of change and maximum values of fault currents. This paper proposes an analytical calculation of pole-to-pole fault currents and the calculation based DC FCL reactor design for MMC-based symmetrical monopole DC grids. The calculation involves solving circuit equations in the time domain to derive mathematical expressions, using MMC fault equivalent model. This calculation enables accurate and fast computation by providing fault current expressions based on circuit parameters. The calculation result is validated through PSCAD/EMTDC simulations.