Rated Wind Speed Research Articles

A fractional order fuzzy-proportional-integral-derivative based pitch angle controller for a direct-drive wind energy system

A wind energy conversion system (WECS) is a highly nonlinear and coupled system in which the output power depends upon highly uncertain wind speed. Therefore, the quality of produced power becomes a challenging problem for engineers. Pitch angle control is a powerful and widely used power control method to handle wind above the rated wind speed. In this paper, a fractional order fuzzy-proportional-integral-derivative controller is proposed for pitch angle control to preserve the output power of a 2 MW direct-drive WECS at the rated value in dynamic wind conditions. To evaluate the performance of the proposed controller, the rise time, fall time, settling time, overshoot and total harmonic distortion by the proposed controller are compared with conventional and other intelligent controllers. Furthermore, the proposed controller is well-tuned using a teaching-learning based optimization (TLBO) algorithm. The performance of the TLBO is also compared with the genetic algorithm to show effectiveness.

Wind turbines power regulation using a low-complexity linear parameter varying-model predictive control approach

In this paper, the model predictive control (MPC) approach is utilized to stabilize the output power of the wind turbines at the region above the rated wind speed. The controller is designed based on two different approaches and results have been compared. First, by putting the advantages of the MPC approach into practice, the optimal output power regulation of the wind turbine is obtained using a control oriented linear parameter varying (LPV) model of the wind turbine. However, this method inherently requires high computational cost and thus powerful hardware and processors. To cope with this limitation, an efficient suboptimal approach is proposed that significantly reduces the online computational complexity of the controller. In this approach, the main part of the controller design procedure is done off-line prior to the closed-loop wind turbine power generation and a set of optimal controllers were designed using the MPC scheme. Then, a convex combination of the calculated controllers is used for online power regulation of the wind turbine. It is noted that the selected wind turbine is a horizontal axis wind turbine operating at various speeds ranging from 10-25 m/s. Finally, using a set of simulation results we investigate the performance of the proposed approach.

Analyses of offshore wind turbine structures with soil-structure interaction under earthquakes

Abstract This research provides an analysis framework for offshore wind turbine (OWT) support structures subjected to seismic, wind, and wave loads using the finite element method with soil-structure interaction, and a conservative soil liquefaction analysis is developed. The NREL 5-MW jacket-type OWT under IEC 61400-3 is analyzed. The results indicate that seismic loads combined with wind and wave loads during power production often control the design, especially near the rated wind speed. For earthquakes with a peak ground acceleration (PGA) smaller than 0.32 g and the dominant period (Ts) smaller than 1 s, the increase in steel weight due to seismic loads is small, because the amplification of the seismic loads is not obvious. For PGA over 0.52 g, almost all the members are controlled by the seismic loads, and the increase in the steel design weight can be over 40%. This paper also indicates that first-mode tuned mass dampers for jacket-type support structure with deep piles are efficient to reduce the vibration coupled from wind, wave, and seismic loads even with 20-m soil liquefaction.

Low‐frequency dynamics of a floating wind turbine in wave tank–scaled experiments with SiL hybrid method

AbstractThe design of floating wind turbines needs the validation of numerical models against measurements obtained from experiments that accurately represent the system dynamics. This requires solving the conflict in the scaling of the hydrodynamic and aerodynamic forces that arises in tests with wind and waves. To sort out this conflict, we propose a hybrid testing method that uses a ducted fan to replace the rotor and introduce a force representing the aerodynamic thrust. The force is obtained from a simulation of the rotor coupled in real time with the measured platform displacements at the basin. This method is applied on a test campaign of a semisubmersible wind turbine with a scale factor of 1/45. The experimental data are compared with numerical computations using linear and non‐linear hydrodynamic models. Pitch decays in constant wind show a good agreement with computations, demonstrating that the hybrid testing method correctly introduces the aerodynamic damping. Test cases with constant wind and irregular waves show better agreement with the simulations in the power spectral density's (PSD's) low‐frequency region when non‐linear hydrodynamics are computed. In cases with turbulent wind at rated wind speed, the low‐frequency platform motions are dominated by the wind, hiding the differences from hydrodynamic non‐linearities. In these conditions, the agreement between experiments using the proposed hybrid method and computations is good in all the frequency range both for the linear and the non‐linear hydrodynamic models. Conversely, for turbulent winds producing lower rotor thrust, non‐linear hydrodynamics are relevant for the simulation of the low‐frequency system dynamics.

Pitch angle control of a wind turbine operating above the rated wind speed: A sliding mode control approach

The paper focuses on variable-rotor-speed/variable-blade-pitch wind turbines operating in the region of high wind speeds, where control is aimed at limiting the turbine energy capture to the rated power value. A robust sliding mode approach is proposed, using the blade pitch as control input, in order to regulate the rotor speed to a fixed rated value, in the presence of uncertainties characterizing the wind turbine model. Closed loop convergence of the overall control system is proved. The proposed control solution has been validated on a 5−MW three-blade wind turbine using the National Renewable Energy Laboratory (NREL) wind turbine simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. A comparison with the standard FAST baseline controller (NWTC 2012 and Jonkman et al. 2009) has been also included.

Modified P&O MPPT algorithm for optimal power extraction of five-phase PMSG based wind generation system

In this study, the maximum power point tracking (MPPT) performance is investigated based on variable-speed wind energy conversion system below the rated wind speed. The proposed modified perturb and observe (MPO) MPPT enhances the initial speed-tracking accuracy and eliminates the oscillations level. The MPO employs four sectors operation using a variable-speed step sizes by comparing the new suggesting curve with the P–ω curve. The system is described as a large-scale five-phase permanent magnet synchronous generator (PMSG) which is grid connected through a back-to-back converter (BTBC) and Dc-link capacitor. The field-oriented control (FOC) is applied in the machine-side converter (MSC) to extract the optimal generated power using the proposed MPPT algorithm. Moreover, the voltage-oriented control (VOC) is applied in the grid-side converter (GSC) to regulate the Dc-link voltage and inject active power with unity power factor. The simulation results depict the superior performance of the MPO over the conventional P&O. The performance of the proposed control scheme is validated using MATLAB/SIMULINK program.

Power dispatching tracking control of wind turbine considering maximum and limited power generation below rated wind speed

Wind turbines should respond to power dispatching of power grid at all times. According to this demand, this paper puts forward a set of feasible power control strategies below rated wind speed. Firstly, the operation state of wind turbine is divided into two working modes: maximum power generation and wind power curtailment generation. Different control strategies are adopted in different working conditions. Under the mode of maximum power generation, the model predictive control (MPC) algorithm is used to give a torque compensation gain. The MPC controller not only improves the utilization efficiency of wind energy, but also reduces the mechanical load. Under the mode of wind curtailment, a hybrid tracking control strategy of giving priority to torque control than pitch regulation is adopted. It reduces the frequency and amplitude of the pitch mechanism greatly. By comparing the simulation results under various wind speeds, it is found that the proposed power control strategy can adapt to different power dispatching scenes, and can respond to power dispatching with greater performance. It is very significant for the improvement of wind power generation system.

Particle swarm optimisation technique to improve energy efficiency of doubly‐fed induction generators for wind turbines

Wind energy conversion systems (WECSs) require a suitable control to maximise the power generated by wind turbines independently on the wind conditions. Variable-speed fixed-pitch wind turbines with doubly-fed induction generators (DGIG) are used in WECSs for their higher reliability and efficiency compared to variable-pitch wind turbine systems. This study proposes an effective control algorithm to maximise the efficiency of fixed-pitch wind turbines with DFIGs using particle swarm optimisation control to compensate for the errors in the estimation of the circuit parameters of the generator. The proposed control algorithm generates an optimal speed reference to optimise the mechanical power extracted from the wind and the optimal d -axis rotor current through stator reactive power management to minimise the electrical losses of the doubly-fed generator. The optimal speed reference is provided by a maximum power point tracking control below the rated wind speed and a soft-stalling control above the rated wind speed, while the optimal d -axis rotor current is searched by a particle swarm optimisation algorithm. The proposed control system has been verified by numerical simulations and it has been demonstrated that the energy generated for typical wind speed profiles is greater than that of a traditional control based on a model-based loss minimisation.

Potential and economic viability of green hydrogen production by water electrolysis using wind energy resources in South Africa

In recent times, more attention is given to renewable and clean energy sources that could ameliorate the current shortage of electricity plaguing South Africa. Due to the comparable use of hydrogen to fossil fuel in the transportation, industrial and electricity sector, hydrogen could be a potential solution to the current energy crises especially when produced from a clean and sustainable source. One of the most appropriate methods of green hydrogen production is the use of wind energy via water electrolysis. This paper therefore investigates the capability and viability of hydrogen production from the wind energy resources of South Africa using the actual wind speed obtained at 60 m anemometer height. Sensitivity analyses are also conducted to gain insight into the possible influences of wind turbine operating parameters on the cost of hydrogen production. Wind regime of fifteen (15) different sites across five (5) major provinces are analysed for possible wind-hydrogen production using eleven (11) different off-the-shelf wind turbines ranging from small to large categories. Some of the key results revealed that the mean wind speed (Vm) varies from 5.07 m/s in Eston (S12) to 8.10 m/s in Napier (S5). Wind turbine WT9 (ServionSE MM100) with rated wind power of 2 MW, cut-in wind speed of 2 m/s, rated wind speed of 11 m/s, cut-out wind speed of 22 m/s and turbine hub-height of 100 m has the highest capacity factor (Cf) across all the sites with the values that range from 24.04% in Eston (S12) to 54.55% in Napier. Site S5 presents the best hydrogen production potential with annual hydrogen production that ranges between 6.51 metric-tons with turbine WT1 and 226.82 metric-tons of hydrogen with turbine WT11. Wind turbine WT9 has the least cost of electricity generation ranging from 0.23$/kwh at site S5 to 0.42 $/kwh at site S13. Also, the cost of hydrogen is lowest at site S5 and ranges between 39.55 $/kg using wind turbine WT1 and 1.4 $/kg using wind turbine WT11. The sensitivity analysis conducted revealed that rated wind speed has significant effect on the cost of hydrogen production compared to other wind turbine parameters.

Extreme wind fluctuations: joint statistics, extreme turbulence, and impact on wind turbine loads

Abstract. For measurements taken over a decade at the coastal Danish site Høvsøre, we find the variance associated with wind speed events from the offshore direction to exceed the prescribed extreme turbulence model (ETM) of the International Electrotechnical Commission (IEC) 61400-1 Edition 3 standard for wind turbine safety. The variance of wind velocity fluctuations manifested during these events is not due to extreme turbulence; rather, it is primarily caused by ramp-like increases in wind speed associated with larger-scale meteorological processes. The measurements are both linearly detrended and high-pass filtered in order to investigate how these events – and such commonly used filtering – affect the estimated 50-year return period of turbulence levels. High-pass filtering the measurements with a cutoff frequency of 1∕300 Hz reduces the 50-year turbulence levels below that of IEC ETM class C, whereas linear detrending does not. This is seen as the high-pass filtering more effectively removes variance associated with the ramp-like events. The impact of the observed events on a wind turbine are investigated using aeroelastic simulations that are driven by constrained turbulence simulation fields. Relevant wind turbine component loads from the simulations are compared with the extreme turbulence load case prescribed by the IEC standard. The loads from the event simulations are on average lower for all considered load components, with one exception: ramp-like events at wind speeds between 8 and 16 m s−1, at which the wind speed rises to exceed rated wind speed, can lead to high thrust on the rotor, resulting in extreme tower-base fore–aft loads that exceed the extreme turbulence load case of the IEC standard.

Development of Hardware-in-the-Loop-Simulation Testbed for Pitch Control System Performance Test

This paper deals with the development of a wind turbine pitch control system and the construction of a Hardware-in-the-Loop-Simulation (HILS) testbed for the performance test of the pitch control system. When the wind speed exceeds the rated wind speed, the wind turbine pitch controller adjusts the blade pitch angles collectively to ensure that the rotor speed maintains the rated rotor speed. The pitch controller with the individual pitch control function can add individual pitch angles into the collective pitch angles to reduce the mechanical load applied to the blade periodically due to wind shear. Large wind turbines often experience mechanical loads caused by wind shear phenomena. To verify the performance of the pitch control system before applying it to an actual wind turbine, the pitch control system is tested on the HILS testbed, which acts like an actual wind turbine system. The testbed for evaluating the developed pitch control system consists of the pitch control system, a real-time unit for simulating the wind and the operations of the wind turbine, an operational computer with a human–machine interface, a load system for simulating the actual wind load applied to each blade, and a real pitch bearing. Through the several tests based on HILS test bed, how well the pitch controller performed the given roles for each area in the entire wind speed area from cut-in to cut-out wind speed can be shown.

A Study on the Effect of Closed-Loop Wind Farm Control on Power and Tower Load in Derating the TSO Command Condition

This study was conducted to analyze the impact of surrounding environmental changes on the feedback gain and performance of a closed-loop wind farm controller that reduces the error between total power output of wind farm and power command of transmission system operator. To analyze the impact of environment changes on wind farm controller feedback gain, the feedback gain was manually changed from 0 to 0.9 with a 0.1 interval. In this study, wind speed and wind direction changes were considered as environment changes; it was found by simulation code that the wind farm controller gain is in inverse proportion to wake recovery rate. In other words, the feedback gain should be higher if the distance between upstream and downstream wind turbine is not sufficient to wake recovery. Furthermore, the feedback gain should be lower when the upstream wind turbine generates a relatively weak wake by operating above the rated wind speed. The wind farm simulation was performed using reference 5 MW wind turbines from the National Renewable Energy Laboratory (NREL), which are numerically modeled for each element so that wind farm power output and tower load can be calculated according to the variation of the power command by using a modified wake model with improved accuracy. All the simulations performed in this study were carried out to review the power output accuracy of wind farms, but only if the transmission system operator’s power command was lower than the available power of wind farm. In this study, the gain of the wind farm controller was applied differently depending on the wind speed and direction to consider benefits in terms of power and tower load, especially if the wake effect of the upstream wind turbine was rapidly transferred to the downstream wind turbine. Ultimately, a simple, but more effective, power distribution method was proposed for distributing power commands to wind turbines that constitute wind farms and the study indicated the need for controller gain adjustment based on surrounding environmental changes.

Investigation on Optimization Design of Offshore Wind Turbine Blades based on Particle Swarm Optimization

Offshore wind power has become an important trend in global renewable energy development. Based on a particle swarm optimization (PSO) algorithm and FAST program, a time-domain coupled calculation model for a floating wind turbine is established, and a combined optimization design method for the wind turbine’s blade is developed in this paper. The influence of waves on the power of the floating wind turbine is studied in this paper. The results show that, with the increase of wave height, the power fluctuation of the wind turbine increases and the average power of the wind turbine decreases. With the increase of wave period, the power oscillation amplitude of the wind turbine increases, and the power of the wind turbine at equilibrium position decreases. The optimal design of the offshore floating wind turbine blade under different wind speeds is carried out. The results show that the optimum effect of the blades is more obvious at low and mid-low wind speeds than at rated wind speeds. Considering the actual wind direction distribution in the sea area, the maximum power of the wind turbine can be increased by 3.8% after weighted optimization, and the chord length and the twist angle of the blade are reduced.

Torque and pitch angle control of a wind turbine using multiple adaptive neuro-fuzzy control

This article presents a multiple adaptive neuro-fuzzy inference system-based control scheme for operation of the wind energy conversion system above the rated wind speed. By controlling the pitch angle and generator torque concurrently, the generator power and speed fluctuation can be reduced and also turbine blade stress can be minimized. The proposed neuro-fuzzy-based adaptive controller is composed of both the Takagi–Sugeno fuzzy inference system and neural network. First, a step change in wind speed and then a simulated wind speed are considered in the proposed adaptive control design. A MATLAB/Simulink model of the wind turbine system is prepared, and simulations are carried out by applying the proportional integral, fuzzy-proportional integral and the proposed adaptive controller. From the obtained results, the effectiveness of the proposed adaptive controller approach is confirmed.

Power curve and wake analyses of the Vestas multi-rotor demonstrator

Abstract. Numerical simulations of the Vestas multi-rotor demonstrator (4R-V29) are compared with field measurements of power performance and remote sensing measurements of the wake deficit from a short-range WindScanner lidar system. The simulations predict a gain of 0 %–2 % in power due to the rotor interaction at below rated wind speeds. The power curve measurements also show that the rotor interaction increases the power performance below the rated wind speed by 1.8 %, which can result in a 1.5 % increase in the annual energy production. The wake measurements and numerical simulations show four distinct wake deficits in the near wake, which merge into a single-wake structure further downstream. Numerical simulations also show that the wake recovery distance of a simplified 4R-V29 wind turbine is 1.03–1.44 Deq shorter than for an equivalent single-rotor wind turbine with a rotor diameter Deq. In addition, the numerical simulations show that the added wake turbulence of the simplified 4R-V29 wind turbine is lower in the far wake compared with the equivalent single-rotor wind turbine. The faster wake recovery and lower far-wake turbulence of such a multi-rotor wind turbine has the potential to reduce the wind turbine spacing within a wind farm while providing the same production output.

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

Gearbox failure is one of the major factors causing the increased downtime in modern wind turbines. This increases the turbine maintenance cost and therefore the turbine cost of energy. A hydrostatic transmission not only improves the turbine reliability through its “soft” transmission, but also eliminates the use of power converter through its continuous variable transmission function. A hydrostatic wind turbine usually employs a fixed displacement pump to drive a variable displacement motor. The variable displacement motor runs at partial displacement when the wind speed is below the rated wind speed, leading to low drivetrain efficiency. Moreover, large variable displacement motors for large utility wind turbine are not commercially available. Therefore in this paper a digital hydrostatic transmission solution for large utility wind turbine has been proposed. The large variable displacement motor was replaced by combining several fixed displacement motors and a small variable displacement motor with some digital encoding scheme. Two encoding schemes have been proposed for digital hydrostatic transmission. The modeling and design of the digital hydrostatic wind turbine were presented. A hydrostatic wind turbine control based on kw2 control law has been proposed. A dynamic simulation model of the digital hydrostatic wind turbine has been developed. The proposed digital hydrostatic drive solution has been compared with a conventional hydrostatic solution in a commercial 2.5 MW wind turbine. Simulation studies verified the feasibility and the engineering practice of the proposed digital hydrostatic drive solution.

A novel method for wind farm layout optimization based on wind turbine selection

A novel method was developed to detect the optimal onshore wind farm layout driven by the characteristics of all commercially-available wind turbines. A huge number of turbine combinations (577) was processed, resulting in 22,721 generated layouts. Various assumptions and constraints were considered, mostly derived from the literature, including site features, wind conditions, and layout design. For the latter, an irregularly staggered turbine array configuration was assumed. Wake effects were simulated through the Jensen’s model, while a typical turbine thrust coefficient curve as a function of wind speed was originally developed. A detailed cost model was used, with levelized cost of energy selected as primary and capacity factor as secondary objective function. The self-organizing maps were used to address a thorough analysis, proving to be a powerful means to straightforwardly achieve a comprehensive pattern of wind farm layout optimization.In general, the two optimization functions basically match, while for higher wind potential sites, increasing capacity factor did not necessarily result in decreasing levelized cost of energy. The latter may be minimised by reducing the total number of turbines or the overall wind farm capacity, as well as maximising rotor diameters or minimising rated wind speeds; increasing rated power or hub height is only beneficial for mid-potential sites. The mere maximisation of wind farm energy production is a misleading target, as corresponding to mid-to-high values of levelized cost of energy. In contrast to previous studies, the use of turbines with different rated power, rotor diameter or hub height should be avoided.

Study on speed and torque control of a novel hydromechanical hybrid transmission system in wind turbine

A wind turbine is the most typical machine used to capture energy from the wind. The system design goal of a wind turbine is to obtain as much energy as possible from the wind while transmitting as much of that energy to the grid as possible, all under the highest possible level of stability. Currently, many inherent weaknesses result in a high failure rate in common commercial wind turbines with gear drive systems. To improve the performance, in this study, a typical 1.5 MW gear transmission was redesigned into a novel hydromechanical transmission system (HMTS). Parameters related to the HMTS efficiency were analysed to ensure that the efficiency was relatively high. The variable speed ratio (VSR) and torque triple absorption (TTA) principle were thoroughly deduced. Moreover, a MATLAB/Simulink- AMESim cosimulation model was proposed, and a 30 kW proportional prototype was established. Both simulation and experimental results show that the structural design and proposed control strategies meet the design goals, including a relatively high transmission efficiency around the rated wind speed, speed control below the rated wind speed, and torque control above the rated wind speed. These achievements should guarantee the future application of the novel transmission system in wind turbines.

Primary frequency control of a microgrid with integrated dynamic sectional droop and fuzzy based pitch angle control

In a microgrid (MG), employing conventional fixed droop gain control of wind turbine for mimicking conventional generators may threaten grid stability. In this paper, an integrated control strategy of inertia emulation and dynamic sectional droop control for generating active power reference of the wind power system is presented to provide primary frequency control (PFC) services. The dynamic sectional droop is implemented with the fuzzy logic controller (FLC) regulated pitch angle control mechanism and compared with the conventional proportional-integral (PI) pitch angle control method in the isolated MG. Two different gain values are selected for developing the proposed sectional droop control which is based on the sensitivity of frequency deviation in comparison to the single fixed gain in conventional droop control. The maximum power margin of wind turbine is considered as 25% and 15% for a wind speed higher than (or equal to) the rated speed and lower than the rated speed, respectively. The effectiveness of the proposed method is investigated through Matlab/Simulink based real-time simulation studies. Simulation results demonstrate that the proposed sectional droop control provides superior performance than conventional fixed-gain method and achieves optimum frequency regulation at the rated wind speed and even for a wind speed lower than the rated wind speed.

Dynamic Modeling and Simulation of a Spar Floating Offshore Wind Turbine With Consideration of the Rotor Speed Variations

This paper presents a rigid multibody dynamic model to simulate the dynamic response of a spar floating offshore wind turbine (FOWT). The system consists of a spar floating platform, the moorings, the wind turbine tower, nacelle, and the rotor. The spar platform is modeled as a six degrees-of-freedom (6DOFs) rigid body subject to buoyancy, hydrodynamic and moorings loads. The wind turbine tower supports rigid nacelle and rotor at the tip. The rigid rotor is modeled as a disk spinning around its axis and subject to the aerodynamic load. The generator torque control law is incorporated into the system dynamics to capture the rotor spinning speed response when the turbine is operating below the rated wind speed. The equations of motions are derived using Lagrange's equation in terms of the platform quasi-coordinates and rotor spin speed. The external loads due to hydrostatics, hydrodynamics, and aerodynamics are formulated and incorporated into the equations of motion. The dynamic simulations of the spar FOWT are performed for three load cases to examine the system eigen frequencies, free decay response, and response to a combined wave and wind load. The results obtained from the present model are validated against their counterparts obtained from other simulation tools, namely, FAST, HAWC2, and Bladed, with excellent agreement. Finally, the influence of the rotor gyroscopic moment on the system dynamics is investigated.