Abstract
The focus of the current paper is on a hydraulic soft yaw system, designed to reduce the loading of the turbine structure, by absorbing wind guest via the hydraulic system, but which also enables the system to be used as a self-aligning yaw system. The system is analyzed with basis in the NREL 5-MW turbine, modeled in FAST, in which a new robust method for implementing Coulomb friction is utilized. Based on this model and a model of the hydraulic system, the influence of friction and wind speed is investigated in relation to the possibility to use the system as a self-aligning yaw system. Similarly the behavior of the hydraulic system is analyzed and it is concluded that the hydraulic yaw system allows self-yaw under normal operating conditions for the turbine. Self-yaw control is possible in wind speeds above 12 m/s when yaw friction is kept below 1 MNm.
Highlights
Considering the yaw system for wind turbines there has not been any significant development within this area for the last 20 years, where a standard system is made as an electrical yaw system, consisting of a number of electrical motors mounted with gear reduction units connected with a pinion-tooth-rim assembly
To indicate that the friction effect behaves as expected a random sample for a 24 [m/s] Normal Turbulence Model (NTM) DLC is shown in figure 3, without any additional control or torque other than the torque from the friction force
It is clear that the load transferred from the nacelle to the tower via the yaw system is limited to ±1000 [kNm], namely the yaw friction
Summary
Considering the yaw system for wind turbines there has not been any significant development within this area for the last 20 years, where a standard system is made as an electrical yaw system, consisting of a number of electrical motors mounted with gear reduction units connected with a pinion-tooth-rim assembly. Considering a traditional yaw system, this operates by releasing the hydraulic yaw brakes and activating the electrical motors when the nacelle needs to be turned This enables one of the possible root causes for yaw systems break down, where the yaw motors are operating in generator mode, in which case the load on the system braking pinion and tooth rim teeth is raised and/or the motors are accelerated to the point of break down. Based on the above ideas a new concept have been developed, which overcome the previously mentioned problems, and which shows very promising results with regard to both load reductions in the turbine structure and which enables passive yawing or self yawing during off-grid operation, using only the loading from the wind to turn the nacelle. With focus on the operating conditions for the hydraulic motors and the system is found to be applicable during erection of the turbine and under grid loss under certain conditions
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