Due to platform motions, floating offshore wind turbine loads are increased. Among proposed platform concepts, tension leg platform introduces least wind turbine load increase. To reduce wind turbine loads, extra actuators have been added to the platform to suppress the tension leg platform motion. For these actuators controller design, it is critical to derive a mathematical model of the platform-wind turbine-actuator system. In this paper, a reduced 13 DOFs model is derived using Lagrange equation and validated with simulation results from FAST. This reduced model is simple, but accurate enough to predict wind turbine and platform response under wind and wave disturbance. Based on the proposed model, an LQR controller is designed. One simulation case shows that the wind turbine tower load can be effectively reduced by actively controlled DVAs.

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