Hydraulic Soft Yaw System for Multi MW Wind Turbines

Research output: ResearchPh.D. thesis

Abstract

Horizontal axis wind turbines utilize a yaw system to keep the rotor plane of the wind turbine perpendicular to the main wind direction. If the wind direction changes, the wind turbine follows the direction change by yawing. If the wind turbine does not yaw, there will be a reduction in produced energy and an increase in the loading of the wind turbine structure and components.

This dissertation examines the hypothesis that there are advantages of basing a yaw system on hydraulic components instead of normal electrical components. This is done through a state of the art analysis followed by a systematic concept generation and analysis of different concepts, where a single concept is chosen for further analysis.

A preliminary analysis, based on simulations of the NREL 5 MW turbine modified to include a soft yaw system, show that the soft yaw concept chosen leads to signicant load reductions in the wind turbine yaw system along with minor reductions in the blades and main shaft. Optimization of the damping and stiffness of the hydraulic soft yaw system have been conducted and an optimum found for load reduction.

Linear control algorithms for control of damping pressure peaks have been developed and tested in simulations with success.

To verify the results of the new hydraulic soft yaw concept a novel friction model for including coulomb in the yaw system is developed and implemented in the FAST aeroelastic code from NREL in order to include friction phenomena. A cosimulation interface between the full turbine code in FAST, and the mathematical model of the hydraulic yaw system in Matlab/Simulink and Amesim is developed in order to analyze a full scale model of the hydraulic yaw system in combination with the implemented friction model for the yaw system. These results are also promising regarding load reduction and operating conditions for the hydraulic components. The results for simulations of a normal stiff yaw system, a yaw system with friction plate yaw bearing and a yaw system with a roller type bearing with low friction are analyzed and so is the loading of the systems.

Based on the results a full scale test rig is designed and constructed for workshop testing and model validation. The test rig is designed so that it is possible to apply loads directly from the FAST simulations and hence get realistic results. Results from the test rig are presented and analyzed and the hydraulic model validated for further testing in the co-simulation environment. All test are performed according to the standard IEC 61400-1; Wind turbines- Part 1: Design requirements, why the load cases may be recognized from this standard.

The model is further used for testing of the developed self yaw system, which enables the turbine to yaw without any energy input, but simply by utilizing the loading from the wind to turn in the right direction. Further the concept of the over-load protection system is analyzed and found very efficient for lowering the ultimate loading on the wind turbine structure.

The influence on the energy capture is analyzed and by the present simulation standards it is hard to quantify the inuence of the soft yaw system, however, the energy capture is increased for situations including a yaw error.

The research documented in this dissertation has contributed with a concept evaluation of nine concepts for hydraulic yaw systems and shown that the loading of the turbine structure may be damped if the yaw system is allowed to deflect under loading. An extensions of the open source wind turbine code FAST of a state of the art wind turbine including the yaw degree of freedom and friction in the yaw bearing has furthermore been made public available. A passive self yaw system has been designed, analyzed and patented for off grid operation and operation above rated wind speed. The positive effects of a well defined over-load protection system has also been analyzed and documented. The conclusion of the research presented in this dissertation is a product ready to be tailored to fit OEM prototype turbines for field tests.
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Details

Horizontal axis wind turbines utilize a yaw system to keep the rotor plane of the wind turbine perpendicular to the main wind direction. If the wind direction changes, the wind turbine follows the direction change by yawing. If the wind turbine does not yaw, there will be a reduction in produced energy and an increase in the loading of the wind turbine structure and components.

This dissertation examines the hypothesis that there are advantages of basing a yaw system on hydraulic components instead of normal electrical components. This is done through a state of the art analysis followed by a systematic concept generation and analysis of different concepts, where a single concept is chosen for further analysis.

A preliminary analysis, based on simulations of the NREL 5 MW turbine modified to include a soft yaw system, show that the soft yaw concept chosen leads to signicant load reductions in the wind turbine yaw system along with minor reductions in the blades and main shaft. Optimization of the damping and stiffness of the hydraulic soft yaw system have been conducted and an optimum found for load reduction.

Linear control algorithms for control of damping pressure peaks have been developed and tested in simulations with success.

To verify the results of the new hydraulic soft yaw concept a novel friction model for including coulomb in the yaw system is developed and implemented in the FAST aeroelastic code from NREL in order to include friction phenomena. A cosimulation interface between the full turbine code in FAST, and the mathematical model of the hydraulic yaw system in Matlab/Simulink and Amesim is developed in order to analyze a full scale model of the hydraulic yaw system in combination with the implemented friction model for the yaw system. These results are also promising regarding load reduction and operating conditions for the hydraulic components. The results for simulations of a normal stiff yaw system, a yaw system with friction plate yaw bearing and a yaw system with a roller type bearing with low friction are analyzed and so is the loading of the systems.

Based on the results a full scale test rig is designed and constructed for workshop testing and model validation. The test rig is designed so that it is possible to apply loads directly from the FAST simulations and hence get realistic results. Results from the test rig are presented and analyzed and the hydraulic model validated for further testing in the co-simulation environment. All test are performed according to the standard IEC 61400-1; Wind turbines- Part 1: Design requirements, why the load cases may be recognized from this standard.

The model is further used for testing of the developed self yaw system, which enables the turbine to yaw without any energy input, but simply by utilizing the loading from the wind to turn in the right direction. Further the concept of the over-load protection system is analyzed and found very efficient for lowering the ultimate loading on the wind turbine structure.

The influence on the energy capture is analyzed and by the present simulation standards it is hard to quantify the inuence of the soft yaw system, however, the energy capture is increased for situations including a yaw error.

The research documented in this dissertation has contributed with a concept evaluation of nine concepts for hydraulic yaw systems and shown that the loading of the turbine structure may be damped if the yaw system is allowed to deflect under loading. An extensions of the open source wind turbine code FAST of a state of the art wind turbine including the yaw degree of freedom and friction in the yaw bearing has furthermore been made public available. A passive self yaw system has been designed, analyzed and patented for off grid operation and operation above rated wind speed. The positive effects of a well defined over-load protection system has also been analyzed and documented. The conclusion of the research presented in this dissertation is a product ready to be tailored to fit OEM prototype turbines for field tests.
Original languageEnglish
PublisherDepartment of Energy Technology, Aalborg University
Number of pages283
ISBN (Print)978-87-92846-16-7
StatePublished - 2013
Publication categoryResearch
ID: 78783665