Effects of DC fault clearance methods on transients in a full-bridge monopolar MMC-HVDC link

Power system transition towards sustainability leads to an increasing number of onshore dc interconnector projects to strengthen highly stressed ac networks. Compared to maritime dc realizations, technical constraints significantly differ as overhead-line utilization becomes feasible and dynamic ac grid support is of higher interest. The latter issue is caused by the replacement of conventional generation with remote renewable sources and novel coverter-type feed-in nodes near the ac load centres. Therefore, mainly to allow dc fault ride-through with continuing ac reactive power support, full-bridge MMC topologies can be utilized in response to significantly higher fault probabilities on overheadline segments. This paper introduces and distinguishes between different active fault clearing strategies based on advanced MMC controls. For a partially cabled MMC-HVDC link implementation insights and system transient investigations are provided, which additionally includes the issue of varying fault detection delays and conventional converter module blocking. Presented simulations are carried out using PSCAD Software and validate the proposed methods.