Characterizing ramp events in floating offshore wind power through a fully coupled electrical-mechanical mathematical model

Abstract

Floating Offshore Wind Turbines (FOWTs) exhibit a noteworthy nonlinear low-frequency dynamic response during rated and higher wind-wave scenarios, leading to a substantial exacerbation of its power characteristics, power stability, and wind energy forecast reliability. This study develops a fully coupled FOWT model to investigate the impact of wind and wave loads on wind power ramp events (WPREs), which integrates mechanical and electrical factors, including a spar buoy FOWT with generator, converter, and aero-hydro-servo-elastic (AHSE) dynamics. Results indicate that the floating structure enables periodic and significant WPREs of FOWTs, as wave load and platform natural motion causing low and ultra-low frequency response. In contrast to bottom-fixed offshore wind turbines (OWT), FOWTs exhibit a supplementary decline in rated power output ranging from 7.9 % to 40.5 % during WPREs. Moreover, ramp peak mainly depends on the aerodynamic loads, but become sensitive to wave loads characterized by wave heights over 2.52 m. FOWT power performance is highly unstable within the rated wind speed range, under WPREs within ultra short time period, resulting in failure to meet grid standards, emphasizing the external need for targeted power compensation and power signal processing. Overall, this study highlights the importance of pitch motion and wave load impact for WPRE study of FOWTs.