Search

Abstract Variable-speed stall-regulated (VS-SR) wind turbines can be designed to produce power as efficiently as variable-speed pitch-controlled (VS-PC) systems. However, amongst the main drawbacks of VS-SR systems high transient power and low predictability have been the primary factors in favour of adopting VS-PC system for multi-MW wind turbines. Cyclic and stochastic loads leading to fatigue failure is one of the prime considerations for large wind turbines. In contrast to the current trend of research, which is focused on load alleviation by integrating active flow controllers, this paper highlights the potential benefits of VS-SR wind turbines in reducing fatigue loads. Adopting the NREL 5 MW wind turbine as the baseline, blades are redesigned for stall-regulation. It is shown that a well-designed VS-SR wind turbine experiences significantly less fatigue loads compared to VS-PC systems. It also results in low power transients near and above rated wind speed. Taking into account added complexity, mass and maintenance costs of wind turbines utilising active flow controllers and in view of the recent progresses that have been made regarding the aeroelastic stability of stalled blades, VS-SR systems seem to have a role to play in the design of future wind turbines. Highlights • The potentials of variable speed stall regulated multi-MW wind turbines in shown. • Aerodynamic insensitivity of stalled blades is utilised to reduce fatigue loads. • Power well-maintained at rated value while operating under highly turbulent winds. • Progressive stall line is a new parameter used for planning aerodynamic sensitivity. [ABSTRACT FROM AUTHOR]

One of the major components of horizontal axis wind turbines is the tower, which supports the weight of the rotor and nacelle as well as the thrust force produced by the rotor. Wind turbine towers are designed for static stability under the axial load, for strength to withstand the cantilever thrust force and for dynamic stability in interaction with rotating rotor and blades. This paper presents the results of a numerical investigation into an innovative wind turbine tower design, using the concept of pre-stressed stayed cross-armed columns. Pre-stressed stayed cross-armed columns restrain the column buckling deformation as a result of the tension in the cables causing compression in the horizontal cross-arms. This essentially decreases the effective length of the column, thereby giving it superior axial load resistance against buckling. [ABSTRACT FROM AUTHOR]

Wind turbine smart blades change their aerodynamic characteristics in response to changes in operating condition, aiming at enhancing the power capture capability or controlling the power and aerodynamic load. Smart blades span a wide range of technologies. Some of these technologies have been proposed and developed specially for wind turbines, while some others have been borrowed from aircraft applications. Adaptive blades, telescopic blades, morphing blades, blades equipped with active control surfaces are some examples of smart blades. This paper presents a summary of wind turbine smart blades and advances in simulation and design of these blades. [ABSTRACT FROM AUTHOR]

Due to substantial generation and demand fluctuations in standalone green microgrids, energy management strategies are becoming essential for the power sharing and voltage regulation purposes. The classical energy management strategies employ the maximum power point tracking (MPPT) algorithms and rely on batteries in case of possible excess or deficit of energy. However, in order to realize constant current-constant voltage (IU) charging regime and increase the life span of batteries, energy management strategies require being more flexible with the power curtailment feature. In this paper, a coordinated and multivariable energy management strategy is proposed that employs a wind turbine and a photovoltaic array of a standalone DC microgrid as controllable generators by adjusting the pitch angle and the switching duty cycles. The proposed strategy is developed as an online nonlinear model predictive control (NMPC) algorithm. Applying to a sample standalone dc microgrid, the developed controller realizes the IU regime for charging the battery bank. The variable load demands are also shared accurately between generators in proportion to their ratings. Moreover, the DC bus voltage is regulated within a predefined range, as a design parameter. [ABSTRACT FROM AUTHOR]

This paper presents the results of an investigation into the performance of different controllers in active load control of wind turbine blades equipped with microtabs. A bang–bang (BB) controller, a linear quadratic regulator (LQR) a proportional integral derivative (PID) and a sliding mode controller (SMC) are synthesised for load alleviation. The performance of the synthesised controllers in load alleviation is evaluated by employing WTAC (Wind Turbine Aeroelastic and Control), a wind turbine simulator incorporating an unsteady aerodynamic module, a structural analysis module and a control module. The variable-speed pitch-controlled NREL-5 MW is adopted as the case study. Using frequency domain analysis it is shown that for the studied case all controllers have more or less the same performance at rejecting the first rotational frequency loads. It is also shown that all controllers are more effective at rejecting loads with lower frequencies. BB and PID controllers, although capable of rejecting low frequency loads, may cause amplification of loads with higher frequencies. Investigating the performance of four controllers at different wind speeds for the studied wind turbine, it is observed that the effectiveness of BB and PID controllers reduces with wind speed but on the other hand SMC and LQR perform better at higher wind speeds. Introducing a new parameter, life index, the performance of different controllers in terms of the actuation wear is investigated. It is shown that LQR cause less actuation wear compared to SMC, while having comparable performance in load alleviation. [ABSTRACT FROM AUTHOR]

Abstract: This paper demonstrates the application of combined analytical/FEA coupled aero-structure simulation in design of bend-twist adaptive blades. A genetic algorithm based design tool, in which the power curve is predicted through a combined coupled aero-structure simulation, has been developed. A bend-twist adaptive blade has been designed to be used on the rotor of a constant speed stall regulated wind turbine. The bend-twist adaptive blade is assumed to be made out of anisotropic composite materials. The designed blade has the same aerofoil and chord distribution as the original blade used on the wind turbine, but with a different pre-twist distribution. The simulated results show a significant improvement in the average power of the studied stall regulated wind turbine when employing the designed adaptive blades. [Copyright &y& Elsevier]

Abstract: This paper presents a method for decoupled design of bend-twist adaptive blades (BTABs) in which the aerodynamic and structural designs take place separately. In this approach the induced twist is considered as an aerodynamic design parameter, whilst its dependency on the structural characteristics of the blade is taken into account by imposing a proper constraint on the structure design. The main advantage of this method is the significant reduction in evaluation time by replacing a finite element analysis (FEA)-based coupled-aero-structure (CAS) simulation in the aerodynamic objective evaluation by a non-FEA-based CAS simulation. Through a re-design case study an ordinary blade has been converted to a BTAB and the efficiency of the method in performing decoupled design of BTABs has been illustrated. [Copyright &y& Elsevier]

Abstract: The simulation of wind turbines with bend–twist adaptive blades is a coupled aero-structure (CAS) procedure. The blade twist due to elastic coupling is a required parameter for wind turbine performance evaluation and can be predicted through a finite element (FE) structural analyser. FEA-based codes are far too slow to be useful in the aerodynamic design/optimisation of a blade. This paper presents a combined analytical/FEA-based method for CAS simulation of wind turbines utilising bend–twist adaptive blades. This method of simulation employs the induced twist distribution and the flap bending at the hub of the blade predicted through a FEA-based CAS simulation at a reference wind turbine run condition to determine the wind turbine performance at other wind turbine run conditions. This reduces the computational time significantly and makes the aerodynamic design/optimisation of bend–twist adaptive blades practical. Comparison of the results of a case study which applies both combined analytical/FEA-based and FEA-based CAS simulation shows that when using the combined method the required computational time for generating a power curve reduces to less than 5%, while the relative difference between the predicted powers by two methods is only about 1%. [Copyright &y& Elsevier]

Abstract: This paper describes mesh sizing functions for discretization of a wind turbine blade as a shell structure. Two different functions, one along the blade span and the other chord-wise, are presented. The effect of the magnitude of the aerodynamic force has been considered in a span-wise mesh sizing function to obtain a force-adaptive mesh generator, applicable when the blade needs to be analysed as a part of an aero-structure problem. The direction of the aerodynamic force has been considered in the chord-wise mesh sizing function to improve the mesh efficiency. Results show a large improvement in the rate of convergence when the direction of the external force contributes towards the chord-wise mesh size. [Copyright &y& Elsevier]

Abstract: An aero-structure code has been developed to predict the performance of a horizontal axis wind turbine (HAWT) with adaptive blades. The code is a combination of an aerodynamic code, an adaptive mesh generator and a finite element code, all developed especially for this purpose. It has been shown that for a high elastic coupling, a coupled aero-structure simulation approach is necessary to have acceptable results while a single step simulation approach can only be used to estimate the blade loading and wind turbine power. [Copyright &y& Elsevier]