Ring DC node configurations for enhanced DC fault protection in multiterminal HVDC networks

This paper proposes a ring dc node configuration for more reliable multi-terminal dc grid fault protection. The proposed ring node is tolerant to the loss of one dc circuit breaker. It results in reduced steady state current flow in node branches relative to a conventional star node connection. This reduces on-state losses of solid-state circuit breakers, as well as any dc-dc converters to be used to administer dc fault blocking in addition to voltage matching. The short circuit breaking capacity of each utilized circuit breaker is also reduced since current stresses are distributed among dc breakers within the ring node. The proposed node configurations are of importance for medium and high voltage dc grids interfacing renewable sources (for example, offshore wind) to the onshore ac grid.