Startup and AC fault ride-through strategy for offshore wind power delivery systems utilizing DRU and MMC

As offshore wind power extends into deeper and more remote seas, HVDC transmission technology has emerged as a key research focus. Among various configurations, the scheme that connects DRU and MMC in parallel on the AC side and in series on the DC side has attracted substantial attention. Compared to the more widely used purely flexible HVDC schemes, this configuration offers smaller size, weight, and cost, as well as better economic benefits. However, the startup process of this configuration is constrained by the unidirectional conductivity of the DRU, and it also faces challenges during AC fault ride-through. This paper investigates the control strategy for the DRU-MMC configuration with parallel AC connections and series DC connections. An economical and reliable startup scheme for the system is proposed, along with an AC fault ride-through strategy for the offshore side. The proposed control strategy is validated through simulations in the electromagnetic transient simulation software PSCAD.