Partial Reconfiguration of Multi-Terminal Bipolar HVDC Systems for Continuous Operation of Offshore Wind Power Plants

High-voltage dc (HVDC) transmission systems are commonly used to connect offshore wind power plants (WPPs) with onshore ac grids. However, conventional half-bridge based modular multilevel converters (MMCs) are vulnerable to dc faults, making it difficult to maintain operation. This is particularly critical for offshore WPPs which depend on the grid voltage maintained by the MMC. If the MMC halts during a dc fault, offshore WPPs may also shut down sequentially. This article proposes a partial reconfiguration method for a multi-terminal bipolar HVDC system to ensure continuous operation of offshore WPPs during dc faults. The proposed method applies the reconfiguration to the offshore terminals, enabling rapid switching of the connection of the offshore WPPs and the half-bridge based MMC from the faulted pole to the healthy pole, maintaining power transmission. On the onshore side, conventional ac circuit breakers are used for fault isolation, simplifying implementation. The combination of these methods enables the continuous operation of the offshore WPP without specialized fault current blocking equipment, such as MMCs with fault blocking capability or high-speed dc circuit breakers. This method helps to improve supply reliability without increasing costs. The proposed method is verified by electromagnetic transient (EMT) simulations.