Real-time hybrid testing of rotor control for a 15 MW floating wind turbine: platform pitch mitigation and rotor-speed stabilisation

Control strategies incorporating platform motion feedback have been developed and demonstrated via hydro-aero-servo-modelling for floating wind turbines to mitigate platform pitch motion and rotor speed variation, with potential benefit to system reliability. The gain-scheduling floating feedback approach has shown distinct advantages over land-based and constant-gain control strategies in mitigating negative aerodynamic damping and reducing rotor speed variation above rated wind speed. Here we demonstrate its efficacy in a hybrid physical system, where the hydrodynamics is modelled physically (with Froude scaling) and the aerodynamics in turbulent wind under rotor control is simulated via the in-house aero-servo solver OREGEN_BEMT. The platform motion is measured optically and fed into the control algorithms in real time. The unsteady turbine thrust is replicated by a thruster at hub height, comprising two drone propellers. The experiments show that platform pitch motions near rated wind speed are markedly reduced by the gain-scheduling approach incorporating floating feedback, with the standard deviation roughly 50% lower than that of conventional land-based control. The rotor speed standard deviation is reduced by approximately 20%, accompanied by a slight increase in mean generator power and slightly reduced variability. This reduction in platform pitch motion is consistent with wind-only tests, indicating that there is no evident degradation in control performance under the tested steep nonlinear wave conditions. Since blade pitch and generator torque variations within appropriate constraints are standard in modern wind turbines, the proposed approach is relatively straightforward to implement. The hybrid testing results provide support for its practical applicability.