Predictive DC Fault Ride-Through for Offshore MMC-Based MT-HVDC Grid

Unscheduled event handling capability and swift recovery from transient events are indispensable study areas to ensure reliability in offshore multi-terminal high voltage direct current (MT-HVDC) grids. This paper focuses on enhancing the reliability of half-bridge modular multilevel converters (HB-MMCs) in MT-HVDC grids by introducing a predictive DC fault ride-through recovery controller and fault separation devices. A novel DC protection-informed zonal DC fault ride-through (DC-FRT) scheme for HB-MMCs is proposed, incorporating a Model Predictive Planner (MPP) for optimized control inputs based on local and inter-station measurements and converter constraints. A Real-Time Digital Simulator (RTDS $^\copyright$ ) environment simulates the approach, which improves lower-level control during fault interruption and suppression by utilizing fault detection and location information. In addition, the study examines two control schemes to assess the impact of communication delays in MT-HVDC grids, a critical factor for system stability and reliability during faults. These schemes include a centralized scheme with delays in input and output signals and a decentralized approach focusing on external signal delays. Both are compared against a baseline centralized control with no delays. These approaches explore alternatives for the placement of the proposed controller, considering potential delays in inter-station high-speed communication. The findings underscore the significance of the proposed DC-FRT control in reinforcing MT-HVDC systems against faults, which contributes to efficient recovery and grid stability.