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DC Fault Current Clearance at the Source Side of HVDC Grid Using Hybrid MMC

This paper proposes a source-side DC fault current clearance scheme for HVDC grids under DC short-circuit faults. The scheme uses half-bridge submodules (HBSM) and full-bridge submodules (FBSMs)-based hybrid modular multilevel converter (MMC). The DC fault current behaviors of the HVDC grid is revealed as a primary criterion for the proposed approach. The additional degrees-of-freedom for control of hybrid MMC are incorporated into the HVDC grid to interrupt the fault current feeding at the source side. During the fault ride-through process, the reactive power compensation is maintained. The proposed method does not need the DC circuit breakers since the current in the fault line can be controlled to zero. The primary and backup protection schemes for hybrid MMC-HVDC grid are proposed. The effectiveness of the method is validated by electromagnetic transient simulations on PSCAD/EMTDC.