Study on distributed power-collection and cascaded boosting-voltage topology and strategy for offshore DC station

Different from traditional concentrated power-collection and boosting-voltage (CPCB) topology adopted by HVDC station, this paper adopts a distributed power-collection and cascaded boosting-voltage (DPCB) topology for offshore DC station to collect DC power and boost DC voltage, which consists of multiple cascaded single active bridges (SABs). It has merits of strong DC-voltage boosting ability, low design difficulty and cost, and low system error rate. Three aspects are studied as follows. First, DPCB topology with its circuit equations is deduced step by step, and its operational mechanism is analysed under phase-shifting control method further. Second, PI control strategy is designed based on system small signal model, and system performance is analyzed by Bode diagram. Third, fault tolerance strategy with predicted power ratio is designed to keep DPCB station from breakdown when some SABs and generators are out of order, and enormous power difference occurs due to the factors of wind turbine location and windward. Finally, the feasibility and effectiveness of designed DPCB station with its strategy are verified by experiment results.