Key challenges and prospects for large wind turbines

Performance evaluation of full-scale tuned liquid dampers (TLDs) for vibration control of large wind turbines using real-time hybrid testing

Improving the reliability and energy production of large wind turbine with a digital hydrostatic drivetrain

Rapid growth in wind generation is accompanied with increasingly large wind turbine sizes. While the large rotor size of utility-scale wind turbines can deliver greater economic benefits, the challenges associated with control system development can get significantly amplified with increases in turbine rotor spans. The aim of this paper is to identify and quantify the trade-offs involved with controlling various conflicting control objectives, such as power output maximisation and mitigation of blade and tower loading, in utility-scale wind turbines. In order to do this, first a comprehensive high-fidelity simulation model of a 6 MW wind turbine is developed. This is followed by the development of a series of rule-based, conventional PI and modern LQR controllers. Each of the controllers is designed separately for various control objectives, both independently and as combinations of control objectives. The controllers are validated on high-fidelity wind turbine model under realistic wind and turbulence conditions. A grading scheme is proposed to score the performance of each controller in meeting control objectives when the wind turbine is operated in a range of wind conditions. As a result, the overall performance of various control methods and the computational cost considerations for the control systems development in large utility-scale wind turbines are established.

Especially for very large wind turbines, flat back thick geometries are very interesting and attractive since they can provide very good structural properties to the blade without dramatically sacrifice the aerodynamic performance in terms of lift. In addition, they help to reduce transportation problems; in fact they are used at the root of the blade where the structural requirements are more demanding and where the maximum chord is located. The present work is focused on the design of thick flat back airfoils. In particular, a new solution is presented and discussed to improve the aerodynamic behavior of the thick sections without sacrifice their structural characteristics. It is known indeed that the flow over these geometries is highly unsteady and the drag is also relevant. The solution presented in the work aims to unsteadiness and drag reduction. A Numerical analysis has been performed by using CFX. According to the results, the new solution has potentialities to reduce significantly the drag and stabilize the flow.

Deep-sea offshore wind resources are extremely abundant. Large offshore wind turbine is the future trend to utilize of deep-sea offshore wind resources. Because of excellent heaving, pitching and rolling performances, tension-leg platform ( TLP ) is one of best floating support structures for large wind turbine. However, under extreme environment condition, the large tendons which are required for large offshore wind turbine TLP platform will meet extreme response, even lead to damage. Extreme response of tendon of a 10 MW offshore wind turbine TLP platform ( an improved MOSES TLP ) in the extreme environment condition is studied here. It is showed that the global motions can meet the basic requirements for 10 MW floating wind turbine, where the maximum angle of TLP is less than 100. Meanwhile, the maximum tendon tension of the TLP in the simulation is less than the breaking force, which meets the requirements of API rules on tendon of TLP.

Observed site obstacle impacts on the energy performance of a large scale urban wind turbine using an electrical energy rose

Presently, wind energy is one of the fastest growing sources in the world. The increase in the size of wind turbines can have significant benefits. By having wind turbines of large capacities, it is possible to reduce the total number of wind turbines needed to produce the same amount of power. Large wind turbines are not suitable for onshore due to transportation and installation limits which is enabled in offshore. Furthermore, floating offshore wind turbine projects have fewer turbines to transport, install and service compared to onshore. University of Ulsan (UOU) has proposed a concept of 12-MW wind turbine. It is now extended to the floating type, where the support structure is scaled up from OC4 semi-submersible platform. This paper aims to design a suitable station-keeping system which is a studless chain catenary mooring system. An in-house code computes suitable positions for anchors and the nominal diameter of mooring chains. The station keeping system is coupled analyzed with the 12 MW floating wind turbine by NREL FAST code. Considering 50 years return period environmental conditions and 20 years operation of wind turbine system, long-term prediction of extreme load of mooring lines are obtained.

Recent years, wind turbine is noted as a renewable energy, and power generation of it increases speedily. Furthermore, power generation of one wind turbine and number of total introduction increases speedily, too. At the same time, the size of wind turbines become larger, and they are constructed not only on the land, but also on the off-shore. Under such circumstance, I suggest the gearless Yaw Axis Swivel Driving System as a new and effective mechanical element for large size wind turbines. And I examined and installed this on the actual wind turbine. In this paper, the result of experimental proof and future prospect are described.

This research describes the development of a test-rig for observing the behavior of a large wind turbine system and investigates the design of power electronics and controller performances in a laboratory environment. The test-rig consists of a PC, Lab Master I/O board, power electronics circuitry and a 3HP separately-excited DC motor which drives a wound rotor induction generator with the rotor windings short circuited. A PC based wind turbine model is employed to simulate the wind turbine behavior where the power coefficient is a function of the pitch angle and tip-speed ratio. A velocity digital PI controller algorithm is adopted for the wind turbine controller to ensure the theoretical rotational speed of a wind turbine rotor by the separately-excited DC motor. The surge current at the motor armature is controlled through algorithm thus avoids any external current limiting circuitry. The system design, model used and preliminary experimental results of the wind turbine test-rig for a wide range of wind speed are presented in the paper.

Since the energy crisis and the environmental issue have been focused due to excessive fossil fuel consumption, the wind power has been considered as an important renewable energy source. Recently, several MW class large scale wind turbine systems have been developed in some countries. Even though the large scale wind turbine can effectively produce the electrical power, the small scale wind turbines have been continuously developed due some advantages, for instance, it can be easily built by low cost without any limitation of location, i.e. even in city. In case of small scale wind turbines, the vertical axis wind turbine (VAWT) is used in city having frequent wind direction change, even though it has a bit lower efficient than the horizontal axis wind turbine. Furthermore, most small scale wind turbine systems have been designed at the rated wind speed of around 12m/s. This work is to design a high efficiency 500W class composite VAWT blade which is applicable to relatively low speed region. In the aerodynamic design of blade, the parametric studies are carried out to decide an optimal aerodynamic configuration. The aerodynamic efficiency and performance of the designed VAWT is confirmed by the CFD analysis. The structural design is performed by the load case study, the initial sizing using the netting rule and the rule of mixture, the structural analysis using FEM, the fatigue life estimation and the structural test. The prototype blade is manufactured by the hand lay-up and the matched die molding. The experimental structural test results are compared with the FEM analysis results. Finally, to evaluate the prototype VAWT including designed blades, the performance test is performed using a truck to simulate the various range wind speeds and some measuring equipments. According to the performance evaluation result, the estimated performance is well agreed with the experimental test result in all operating ranges.

SummaryWind energy has shown a remarkable potential for fulfilling the increasing world's energy demand in a clean and sustainable way. The wind energy industry has installed increasingly sophisticated and larger wind turbines particularly in offshore regions to capture such energy as efficiently and cost effectively as possible. The rapid growth in size and capacity of wind turbines together with harsh climate conditions and limited accessibility in offshore regions all result in higher failure rates and increased maintenance requirements and costs. Such difficulties motivate the use of advanced fault detection and diagnosis and fault‐tolerant control schemes in wind farms to improve their reliability and availability. Given the importance of this issue, this paper uses a fuzzy model reference adaptive control approach in a cooperative framework that is oriented to the design and development of a novel fault‐tolerant cooperative control scheme in a wind farm. This scheme handles decreased power generation faults in a wind farm caused by turbine blade erosion and debris buildup on the blades over time. The effectiveness and performance of the proposed scheme is demonstrated by a series of simulations on an advanced large offshore wind farm benchmark model in the presence of wind turbulence, measurement noise, load variations, and realistic fault scenarios.

Large scale wind power has impact on the power system's security and stability. For a large scale wind turbines tripping off accident happening in the region of Guyuan in North China, this paper explains the accident development process, analyzes the main reason for the cascading wind turbines tripping off, builds the simulation model according to the actual data of the North China Grid and the wind power integration system, and reconstructs the accident process based on the simulation, discusses the countermeasures to avoid this kind of cascading accident.

The current tendency of the development of wind power technology is that the variable wind turbines adjust the speed of wind rotor at real time in accordance with wind speed to absorb wind energy more effectively and improve the operating condition of power chain. A critical point of the design of variable wind turbines is to settle the influence of wind speed changes on the smooth electric power output and power driving chain. Based on the differential planet gear system, this paper gives a research on a kind of power splitting driving chain (PSDC), with the basic thought as follow: The wind rotor linked by planet gear frame axis functions as the main power input terminal; Both a main generator and an auxiliary one are adopted in the double degree of freedom planet gear mechanism; The main generator is driven by gear ring of the planet gear mechanism to realize most of energy conversion in the power driving chain and the electric-energy output to the power grid; the auxiliary generator linked by the sun gear serves as the servo element of PSDC. Meanwhile, the servomotor links the supply grid with bi-efficacy of generator and motor under the control of small electronic power devices, achieving the control of electromagnetic torque and the constant-speed operating function of main generator. The analysis in this paper shows that the large variable wind turbines consisting of this kind of power splitting driving chain (PSDC) could provide new solutions for those problems with which variable wind turbines are confronted, such as difficulties in the design and manufacture of special large generator, its extortionate cost, the high price of electronic power system for high power conversion and control, as well as the mutual influence between wind turbine unit and supply grid.

Wind turbines are operating under very complex and uncontrolled environmental conditions, including atmospheric turbulence, atmospheric boundary layer effects, directional and spatial variations in wind shear, etc. Over the past decades, the size of a commercial wind turbine has increased considerably. All the complex and uncontrolled conditions mentioned above result in uncertainties of aerodynamic loads calculation on very large wind turbine blades and thus better numerical codes are needed for predicting the loads in the design phase. With the aim to eliminate these uncontrolled effects and improve the aerodynamic models, in last decades, several important experimental campaigns of different wind turbine models have been performed in large wind tunnels. The objective of such experiments (e.g. using the NREL wind turbine and the MEXICO rotor) is to provide high quality measurement data which can be used to validate numerical models and improve different fidelity numerical codes, particularly for predicting wind turbine aerodynamic loads.

Large scale wind turbines and wind farms continue to evolve mounting 94.1GW of the electrical grid capacity in 2007 and expected to reach 160.0GW in 2010 according to World Wind Energy Association. They commence to play a vital role in the quest for renewable and sustainable energy. They are impressive structures of human responsiveness to, and awareness of, the depleting fossil fuel resources. Early generation wind turbines (windmills) were used as kinetic energy transformers and today generate 1/5 of the Denmark’s electricity and planned to double the current German grid capacity by reaching 12.5% by year 2010. Wind energy is plentiful (72 TW is estimated to be commercially viable) and clean while their intensive capital costs and maintenance fees still bar their widespread deployment in the developing world. Additionally, there are technological challenges in the rotor operating characteristics, fatigue load, and noise in meeting reliability and safety standards. Newer inventions, e.g., downstream wind turbines and flapping rotor blades, are sought to absorb a larger portion of the cost attributable to unrestrained lower cost yaw mechanisms, reduction in the moving parts, and noise reduction thereby reducing maintenance. In this work, numerical analysis of the downstream wind turbine blade is conducted. In particular, the interaction between the tower and the rotor passage is investigated. Circular cross sectional tower and aerofoil shapes are considered in a staggered configuration and under cross-stream motion. The resulting blade static pressure and aerodynamic forces are investigated at different incident wind angles and wind speeds. Comparison of the flow field results against the conventional upstream wind turbine is also conducted. The wind flow is considered to be transient, incompressible, viscous Navier-Stokes and turbulent. The k-ε model is utilized as the turbulence closure. The passage of the rotor blade is governed by ALE and is represented numerically as a sliding mesh against the upstream fixed tower domain. Both the blade and tower cross sections are padded with a boundary layer mesh to accurately capture the viscous forces while several levels of refinement were implemented throughout the domain to assess and avoid the mesh dependence.