Control-based fault current limiter for modular multilevel voltage-source converters

The sharp rise in short-circuit currents of voltage-source converters is still a challenge for DC grid reliability, which imposes stringent requirements on DC breakers. Therefore, fault current limiters are used for slowing down the rise in short-circuit currents. This paper proposes a control-based fault current limiter (CbFCL) for modular multilevel converters (MMCs). The proposed method reduces the fault current purely by control action, thus not incurring costs and not leading to reduced stability, energy storage, conduction losses or the need for maintenance as impedance-based fault current limiters do. The CbFCL does not affect the system in normal operation, acting only in the presence of a fault. The CbFCL performance was evaluated performing simulations of a four terminal DC grid. The results confirmed that the CbFCL was able to limit the fault current of the MMC while keeping the AC currents within their nominal limits, and thus producing a minor impact on the grid operation.