Response Analysis and Comparison of a Spar-Type Floating Offshore Wind Turbine and an Onshore Wind Turbine under Blade Pitch Controller Faults

This paper analyses the effects of three pitch controller faults on the responses of an onshore wind turbine and a spar-type offshore floating wind turbine. These faults include: a stuck blade pitch actuator, a fixed value fault and a bias fault of the blade pitch sensor. The faults are modeled in the controller dynamic link library and a short-term extreme response analysis is performed using the HAWC2 simulation tool. The main objectives of this paper are to investigate how different faults affect the performance of wind turbines for condition monitoring purposes and which differences exist in the structural responses between onshore and offshore floating wind turbines. Statistical analysis of the selected response parameters are conducted using the six 1-hour stochastic samples for each load case. For condition monitoring purpose, the effects of faults on the responses at different wind speeds and fault amplitudes are investigated by comparing the same response under normal operation. The severities of the individual faults are categorized by the extreme values of structural loads and the structural components are sorted based on the magnitude of the fault effects on the extreme values. The pitch sensor fixed value fault is determined as the most severe fault case and the shaft appears as the structural component that experiences the highest risk. The effects of fault conditions on the offshore floating and the onshore wind turbines are compared to investigate the potential differences. The results show that faults cause more damage to the tower and the yaw bearing for the onshore wind turbine and more damage to the shaft for the offshore floating wind turbine

Investigation of a medium-sized floating offshore wind turbine with stall regulation

The thesis begins with the development of a stall control concept for a variable-speed medium-sized floating offshore wind turbine. Firstly, the control and protection concepts were developed to ensure the highest possible efficiency throughout the operation. Secondly, fully integrated aero-hydro-servo-elastic simulations were performed to characterize the global dynamic response of the system, identify the design driving loads, and highlight the impacts brought about by the floating support structure

MARE-WINT: New Materials and Reliability in Offshore Wind Turbine Technology

renewable; green; energy; environment; law; polic

Reducing tower fatigue through blade back twist and active pitch-to-stall control strategy for a semi-submersible floating offshore wind turbine

The necessity of producing more electricity from renewable sources has been driven predominantly by the need to prevent irreversible climate chance. Currently, industry is looking towards floating offshore wind turbine solutions to form part of their future renewable portfolio. However, wind turbine loads are often increased when mounted on a floating rather than fixed platform. Negative damping must also be avoided to prevent tower oscillations. By presenting a turbine actively pitching-to-stall, the impact on the tower fore–aft bending moment of a blade with back twist towards feather as it approaches the tip was explored, utilizing the time domain FAST v8 simulation tool. The turbine was coupled to a floating semisubmersible platform, as this type of floater suffers from increased fore–aft oscillations of the tower, and therefore could benefit from this alternative control approach. Correlation between the responses of the blade’s flapwise bending moment and the tower base’s fore–aft moment was observed with this back-twisted pitch-to-stall blade. Negative damping was also avoided by utilizing a pitch-to-stall control strategy. At 13 and 18 m/s mean turbulent winds, a 20% and 5.8% increase in the tower axial fatigue life was achieved, respectively. Overall, it was shown that the proposed approach seems to be effective in diminishing detrimental oscillations of the power output and in enhancing the tower axial fatigue life

Estimation of Extreme Load Responses in a Gearbox of 10-MW Floating Offshore Wind Turbine

This thesis studies the extreme load responses experienced by a 10-MW floating wind turbine situated in the North sea. With a plan to minimise fossil fuels and redefine the energy sector by adopting more safe, efficient, and cleaner solutions, countries have started investing in wind energy to harness the enormous untapped potential contained in the wind. Developing countries have begun building wind turbines to meet their energy needs. Countries started moving away from hydrocarbon and investing more in offshore wind turbines and solar energy parks to meet the expanding population needs and economy and reach net zero emission by 2050. The global average wind turbine size increased from 1.5-MW to 7.58-MW from 2000 to 2020. The future of wind turbines will be in 10-MW to 15-MW class wind turbines as the scientific research community has started to analyse more about the large offshore wind turbine(OWT). The gearbox is considered one of the most critical components in a wind turbine that drives a significant part of operating expenses. Reliability of the gearbox is often crucial for wind turbines which comes as a package with an efficient design and proper load estimation matching the ULS (Ultimate Limit State) condition. The costs of gearbox repair and upkeep and the costs of output losses associated with faulty gearboxes account for a significant portion of the operating costs of the offshore wind turbine. In this thesis, the accuracy and robustness of ACER (Average Conditional Exceedance Rate) as a tool are analysed to estimate extreme loads on the wind turbine gearbox and structure. This is done by analysing varying quantities of accessible data from the North Sea, where most large floating wind turbines are installed. The extreme loads estimated are compared with the Gumbel method under operating conditions of 8m/s, 12 m/s and 16m/s wind speed representing below, rated and above rated wind speed. It is vital to analyse the extreme loads under the dynamics operating condition and analyse the response in a fully coupled state. The aim is to show the accuracy and reliability of ACER in estimating the extreme load’s responses and 1,2 & 5 year return period of large OWT. The results show that the extreme loads’ responses on the 10-MW wind turbine gearbox and structure estimated by ACER gave more accurate and reliable values independent of other extreme value prediction methods like the Gumbel method. This study develops and estimates load responses in large OWT and guides the ultimate limit state load (ULS) calculation for 10-MW wind turbines

Wind Turbine Controls for Farm and Offshore Operation

Development of advanced control techniques is a critical measure for reducing the cost of energy for wind power generation, in terms of both enhancing energy capture and reducing fatigue load. There are two remarkable trends for wind energy. First, more and more large wind farms are developed in order to reduce the unit-power cost in installation, operation, maintenance and transmission. Second, offshore wind energy has received significant attention when the scarcity of land resource has appeared to be a major bottleneck for next level of wind penetration, especially for Europe and Asia. This dissertation study investigates on several wind turbine control issues in the context of wind farm and offshore operation scenarios. Traditional wind farm control strategies emphasize the effect of the deficit of average wind speed, i.e. on how to guarantee the power quality from grid integration angle by the control of the electrical systems or maximize the energy capture of the whole wind farm by optimizing the setting points of rotor speed and blade pitch angle, based on the use of simple wake models, such as Jensen wake model. In this study, more complex wake models including detailed wind speed deficit distribution across the rotor plane and wake meandering are used for load reduction control of wind turbine. A periodic control scheme is adopted for individual pitch control including static wake interaction, while for the case with wake meandering considered, both a dual-mode model predictive control and a multiple model predictive control is applied to the corresponding individual pitch control problem, based on the use of the computationally efficient quadratic programming solver qpOASES. Simulation results validated the effectiveness of the proposed control schemes. Besides, as an innovative nearly model-free strategy, the nested-loop extremum seeking control (NLESC) scheme is designed to maximize energy capture of a wind farm under both steady and turbulent wind. The NLESC scheme is evaluated with a simple wind turbine array consisting of three cascaded variable-speed turbines using the SimWindFarm simulation platform. For each turbine, the torque gain is adjusted to vary/control the corresponding axial induction factor. Simulation under smooth and turbulent winds shows the effectiveness of the proposed scheme. Analysis shows that the optimal torque gain of each turbine in a cascade of turbines is invariant with wind speed if the wind direction does not change, which is supported by simulation results for smooth wind inputs. As changes of upstream turbine operation affects the downstream turbines with significant delays due to wind propagation, a cross-covariance based delay estimate is proposed as adaptive phase compensation between the dither and demodulation signals. Another subject of investigation in this research is the evaluation of an innovative scheme of actuation for stabilization of offshore floating wind turbines based on actively controlled aerodynamic vane actuators. For offshore floating wind turbines, underactuation has become a major issue and stabilization of tower/platform adds complexity to the control problem in addition to the general power/speed regulation and rotor load reduction controls. However, due to the design constraints and the significant power involved in the wind turbine structure, a unique challenge is presented to achieve low-cost, high-bandwidth and low power consumption design of actuation schemes. A recently proposed concept of vertical and horizontal vanes is evaluated to increase damping in roll motion and pitch motion, respectively. The simulation platform FAST has been modified including vertical and horizontal vane control. Simulation results validated the effectiveness of the proposed vertical and horizontal active vane actuators