Approaches to Control and Protection in Offshore VSC-HVDC Links

The paper delves into the challenges of Voltage Source Converter – High Voltage Direct Current (VSC-HVDC) links connecting offshore wind farms (OWF) to the national power grid. A brief review on control and protection functions in VSC-HVDC links, taking into account European and American regulation and grid codes, is conducted. Maintaining frequency, voltage and synchronism setpoints constant at the point of common coupling involves cascade control and protection mechanisms on the AC substations and converters of the offshore wind farm. In this paper, an offshore VSC-HVDC link for a future Black Sea OWF connected to the Romanian power grid is considered. A symmetrical monopolar configuration, together with modular multilevel converters (MMCs) in the connecting substations of the DC link, have been chosen. A case study on power control and the differential current protection system for the onshore substation, designed according to the particularities of the Romanian power transmission network, is proposed.