Control co-design of floating vertical-axis wind turbines

This study addresses the definition and identification of coupling characteristics in floating offshore wind turbine (FOWT) integrated design and derives control co-design (CCD) insights associated with the distinct physical characteristics and control architecture of floating vertical-axis wind turbines (FVAWTs). An integrated aero-servo-hydro-elastic CCD framework is developed for FVAWTs, incorporating coordinated variable-speed variable-pitch (VSVP) control for tower and platform CCD analysis. Results show that the coupling characteristics of integrated design problems can be characterized by governing constraints identified from critical constraints through analysis of optimization history. These constraints provide a quantitative basis for characterizing coupling intensity and for evaluating the actual role of controller participation through its effect on the corresponding response quantities. As the design problem shifts from a single governing constraint to joint restriction by multiple constraints, further constraint relaxation produces nonlinearly diminishing objective improvement, reflecting stronger coupling. FVAWT results reveal CCD behavior distinct from that reported in existing floating horizontal-axis wind turbine (FHAWT) studies, arising from azimuth-dependent aerodynamic forcing, distributed load transfer through blade–tower support structures, and coordinated VSVP control using preoptimized pitch trajectories. These factors lead to local stability constraints near the tower bottom, limited regulation of instantaneous aerodynamic force variations, a platform pitch restoring requirement comparable to that of FHAWTs, and stronger overload suppression with stable rated power regulation, accompanied by higher pitch actuator activity. This study advances the interpretation of controller participation in FOWT integrated design from comparisons of final optimization outcomes to process analysis based on governing constraints, and deepens the understanding of integrated design characteristics of FVAWT systems.