Experimental validation of frequency control from offshore wind power plants in multi-terminal DC grids

This paper presents two methods for frequency control of onshore AC grids from offshore wind power plants (OWPPs) connected to a multi-terminal DC (MTDC) grid. The first method is based on communicating the onshore frequency to the OWPP and the other voltage source converters (VSCs) in the MTDC grid.

The second method is based on a coordinated strategy between the VSCs in the MTDC grid, where the onshore frequency is replicated at the offshore grid using additional control blocks implemented locally at the VSCs of the MTDC grid. The proposed control methods are first verified through simulations on a test set up with an OWPP connected to a three-terminal DC grid using DIgSILENT PowerFactory and then validated experimentally on a laboratory scaled three-terminal DC grid.

The simulation and experimental results prove that, with the proposed control strategies, OWPPs and the VSCs in the MTDC grid can participate in frequency control and support the onshore grid frequency stability.