Multi-source Communication-less Coordinated Frequency Support of DRU-HVDC-based Offshore Wind Power Integration Systems

This paper presents a frequency support strategy for the diode rectifier unit (DRU)-high-voltage direct current (HVDC)-based offshore wind power integration system, which coordinates multiple power sources without communication to reduce receiving grid frequency fluctuations. First, based on the deduced DRU's frequency transfer characteristic, a fine-designed ripple carrying frequency information is superimposed on the HVDC link, transferring the onshore frequency to offshore wind turbines (WTs) via the DC ripple and coupled AC harmonic without communication. Second, multiple power sources are utilized for frequency support, including HVDC capacitance and grid-forming WTs combined with energy storage systems, and appropriate sources are activated in the order specified by the designed thresholds. Finally, the effectiveness of the proposed frequency support strategy is verified by simulations in PSCAD/EMTDC.