Gyrostabilizer based active control of pitch motion for floating offshore wind turbine

To mitigate the pronounced platform pitch motion and tower fore-aft vibration of floating offshore wind turbine (FOWT) under external excitation, an active control strategy for FOWT based on gyrostabilizer is investigated in this paper. Taking the Spar-type FOWT as an example, a five degrees of freedom (DOF) nonlinear coupled model including platform surge, heave, pitch, tower top fore-aft vibration, and gyro precession is established using the Euler-Lagrange equations and validated against OpenFAST. Statistical linearization is employed to derive a load-case-dependent equivalent state-space model while retaining the principal coupling terms, and a genetic-algorithm-optimized linear quadratic regulator is developed for active control while balancing pitch suppression, control effort and precession safety. Sensitivity analyses examine excitation conditions and key gyrostabilizer parameters. Compared with passive control, active control increases the platform pitch standard deviation suppression rate from 70.76% to 83.43% under severe wave excitation and from 39.52% to 43.10% under combined wind-wave excitation. At the same flywheel speed of 4000 rpm, active control also increases the torque-motion matching coefficient from 0.5801 to 0.6563 and from 0.5671 to 0.5988. The proposed strategy enhances stochastic pitch mitigation, torque-motion coordination, and adaptability to environmental excitation.