Adaptation of Controller Concepts for Support Structure Load Mitigation of Offshore Wind Turbines

Different controller concepts can be employed for the support structure load reduction of offshore wind turbines, however, they entail unfavorable collateral effects like additional actuator wear or load fluctuations in other turbine components. Hence, there is a need to identify possibilities of employing such controller concepts only under particular loading and operational conditionse.g. sea states with high waves or large wind-wave misalignment when their load reduction potential is high in relation to their unfavorable side effects. This paper introduces a multi-objective optimization method to perform a trade-off analysis between the reduction of damage equivalent fatigue loads at the monopile support structure and the collateral effects of the different controller concepts. The optimization is performed considering the baseline controller, plus tower fore-aft controller to reduce the tower fore-aft bending moment and the active generator torque controller to reduce the side-to-side load. These two concepts increase the pitch activity and drive train torque variability as collateral effect, respectively. With the optimization methodology presented, it is possible to identify the most efficient operation time to activate different control concepts under each load case, utilizing their advantageous load reduction while limiting their penalty in collateral effects.