Abstract
A comprehensive process of the control and protection against a DC fault in a voltage source converter (VSC) based high-voltage direct current (HVDC) system typically includes fault detection, fault isolation and system recovery. Regarding an offshore wind farm (OWF) integrated modular multilevel converter (MMC) based multi-terminal HVDC (MTDC) system with two control paradigms, i.e. master-slave control and droop control under DC faults, this paper presents the fault isolation, including the isolation of the faulted line section, with detailed control and protection sequence, which would be useful for practical engineering. The control and protection sequence at the system recovery/reconfiguration phase is comprehensively investigated, which includes: (1) when to start the recovery/reconfiguration control; (2) the sequence between deblocking the MMCs and reclosing the AC circuit breakers (AC CBs); and (3) the recovery sequence of each HVDC terminal. Based on the analysis of the system characteristics, a preferred recovery/reconfiguration scheme is proposed. Simulation results on the real-time digital simulator (RTDS) validate the proposed scheme and demonstrate the advantages through comparison with a different recovery sequence. The impact of transient and permanent DC faults on the system recovery/reconfiguration control is discussed. In addition, the recovery/reconfiguration control of the MTDC in radial and meshed topologies is compared and demonstrated. Based on the analytical and simulation studies, a general guideline on the recovery/reconfiguration control of MMC MTDC systems is proposed.
Highlights
Intensive research has been conducted on the control and protection against DC faults for the VSC based HVDC grids
A DC fault could be isolated by tripping the AC CBs and the faulted line section could be isolated by opening DC disconnec
This paper has investigated the control and protection sequence of an offshore integrated MMC MTDC system with two control paradigms, master-slave control and voltage droop control, under DC fault conditions
Summary
Intensive research has been conducted on the control and protection against DC faults for the VSC based HVDC grids. Regarding the offshore integrated MTDC network, emphasis has been predominantly put on the grid integration of the OWFs [18,19], while less attention has been paid to the control and protection of the system following DC faults and the recovery/ reconfiguration control after the clearance/isolation of the fault. The use of DC-DC converters, full-bridge/hybrid MMCs and hybrid DC CBs could become applicable in operation and may be more effective in dealing with DC faults in the future, it is necessary to comprehensively investigate a feasible control and protection strategy before they could become commercially available and viable.
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