Principle and Implementation of Active Ground Fault Arc Suppression Based on Hybrid MMC in AC/DC Distribution Network

A single-phase-to-ground (SPG) fault in a neutral non-effectively grounded AC distribution network may cause the arc at the fault point and a power supply interruption, permeating the zero-sequence voltage into the DC network and the nonfault AC-side of AC/DC hybrid distribution networks (HDNs). This paper proposes a flexible control method for a modified hybrid modular multilevel converter (HMMC), incorporating an additional full-bridge submodules (FBSM) cluster at its DC side, to deal with SPG faults in HDN. The HMMC includes a modified modular multilevel converter with a zero-sequence current flow path to realize active ground fault arc suppression (AGAS) and an FBSM cluster in its DC side to block the zero-sequence component to the DC grid and the non-fault circuits of HDN. The operation principles of the HMMC that achieves AGAS and zero-sequence voltage transmission suppression (ZVTS) are presented. The HMMC can realize AGAS when there is an SPG fault on the AC side, and ZVTS can be realized on the DC side by utilizing the FBSM cluster. The flexible control method proposed herein can ensure the normal operation of the HMMC under SPG fault conditions, achieve power transfer during fault current suppression, and realize ZVTS during arc suppression. Simulation and experimental results verify the feasibility and validity of the proposed HMMC and its flexible control method.