Equivalent circuit for half-bridge MMC dc fault current contribution

The modular multilevel converter (MMC) is currently the preferred converter topology for HVDC point-to-point links and the likely choice for future meshed HVDC grids. For breaker dimensioning or protection system design, thorough knowledge of the dc fault currents supplied by these converters is required. In this paper, the dc fault current supplied by the half-bridge MMC is analyzed and an equivalent circuit model is proposed. The proposed equivalent circuit has a low complexity and accurately models the MMC's contribution to dc faults. Furthermore, the paper proposes guidelines for the values of the equivalent circuit's parameters. Study results show that a high level of accuracy is achieved for a wide variation in converter and fault parameters.