Yaw motion of floating wind turbine platforms induced by pitch actuator fault in storm conditions

Abstract

The paper discusses the factors affecting the large amplitude yaw responses of the DeepCwind wind turbine platform in storms with a faulty blade pitch actuator. The behaviour in operational and storm conditions without faults is provided as a base of comparison. They are followed by the responses to 50-year extreme values defined by the IEC standards, North Sea statistics, and Portugal's coastal storm data. All environmental conditions are head waves upwind sets, presumably causing minimal yaw excitation despite differing in wave excitation frequencies and maximum wind speeds. These scenarios are expanded further to cases where one of the pitch actuators stops functioning and fails to feather the blade. The result reveals large angle yaw motions of the platform. The reasoning behind this motion is explained and a possible method of mitigation through a revision of the HSS brake capacity is discussed. In this process, a frequently applied form of the hydrostatic matrix is reviewed as it includes overlooked coupling terms.