Study on modelling and its parameter estimation of a multibladed windmill

The paper presents a modelling technique and a method for determination of the windmill torque loss coefficients of a multibladed windmill. First, a new model is presented of a multibladed windmill, and the windmill torque loss coefficients are defined. Next, a measuring method based on a recursive estimation technique is developed for determination of the values of these coefficients. The torque loss coefficients are estimated satisfactorily from the simulated data and experimental data for changes in wind speed. The validity of the windmill model and the proposed estimating technique are demonstrated.     

Implementation of a torque and a collective pitch controller in a wind turbine simulator to characterize the dynamics at three control regions

As the capacity of wind turbines has increased, the loads on crucial components such as a gearbox, a generator, and blades are significantly increasing. An intelligent online monitoring system is indispensable to protect the excessive load on core components and manage a wind farm efficiently. In order to verify new online monitoring and diagnostic methods for such a monitoring system in advance, a wind turbine simulator is essential. For this purpose, we developed a simulator that has similar dynamics to an actual 3 MW wind turbine, and is thereby able to acquire a state of operation that closely resembles that of the 3 MW wind turbine under a variety of wind conditions.This paper describes the implementation of a torque and a collective pitch controller, which is used for a new type of simulator with the intention of exploiting online monitoring and diagnostic methods. The torque and the collective pitch controllers were developed to facilitate variable speed-variable pitch control strategies in the wind turbine simulator. Experiments demonstrated that three control regions were successfully deployed on the simulator, and thereby the simulator was operated at all control regions in a stable and accurate manner. Moreover, the strain and vibration measured from the blade and the gearbox showed different trends at three control regions. Therefore, a new type of simulator is an effective means to develop diagnostic and prognostic algorithms as well as online monitoring methods reflecting the dependency of dynamic characteristics on the control regions.     

Experimental study on blade pitch angle effect on the performance of a three‐bladed vertical‐axis Darrieus hydro turbine

Because of higher concerns about increasing global warming, energy consumption and reduction of conventional energy resources and growing attention are given to renewable energy and to cross flow turbines such as the Darrieus turbine to harness water energy (water currents, reservoirs, rivers, and oceans). The aim of the experimental investigation presented in this paper is to evaluate the effect of hydro Darrieus turbine blades fixation pitch angle “i_g” on its performance. Four main sets of experimental tests were conducted for the same vertical‐axis hydro turbine model (VAHT) with four blade fixation pitch angles (i_g = ?1.75°, ?4.5°, 1.75°, and 4.5°), at various water flow velocities (V = 0.3‐0.64 m/s corresponding to a water free flow Reynolds number of 2.5 × 10⁴ to 4.36 × 10⁴). A comparison between the results of the present work and with those of a previous experimental study for i_g = 0° shows that the best performance of the tested turbine is obtained when the blades are set at a pitch angle of 1.75°. In fact, the corresponding optimum mechanical power and power coefficient relative increases are respectively as much as 82% and 67% with respect to i_g = 0° at V = 0.37 m/s and as much as 65% and 77% at V = 0.46 m/s. The worst performance is obtained for the negative blades fixation pitch angle of ?4.5°; at the water flow velocity of 0.37 m/s, this leads to power, and power coefficient relative decreases respectively about 75% and 81% with respect to the results obtained for i_g = 1.75° and respectively about 54% and 68% of those obtained in the previous work for i_g = 0°.     

风电场采用健康系数与变下垂输出系统参与电网调频研究

针对风电场参与电网调频导致备用功率冗余的问题,建立了风电场基于健康系数的备用功率分配系统与变下垂系数的备用功率输出的系统。为了分配风机备用功率与控制风机备用功率输出,采用了ARMA风功率预测法对风电场5台风机的历史功率数据进行处理,得到风机的能量密度和功率预测准度,再通过模糊逻辑系统求得风机健康系数,并按照健康系数进行备用功率分配。当频率响应系统检测到频率误差后,控制风机变下垂功率输出系统进行功率补偿,稳定电网频率。仿真结果表明,基于健康系数的功率分配系统与变下垂功率输出系统增加了风电参与电网调频的能力,减少了系统备用功率的冗余。     

Dynamic response analysis of wind turbines under blade pitch system fault,grid loss,and shutdown events

This study focuses on the dynamic responses of land‐based and floating wind turbines under blade pitch system fault and emergency shutdown conditions. The NREL 5 MW turbine is studied. A hydraulic pitch system is considered, and the faults under study are events with a seized blade or a blade running out of control. Emergency shutdown is defined as a fast pitch‐to‐feather maneuver of the blades. Load cases with power production and grid fault with ensuing shutdown are also analysed for comparison. The fault scenarios and the blades' fast pitching activity are simulated using HAWC2 through external Dynamic Link Libraries. On the basis of the time‐domain simulations, the response characteristics of the land‐based and the floating turbines in the four design load cases are compared. The load effects from the fault conditions are compared with the operational cases. Strong system dynamics and resonant responses, such as the tower elastic mode and the yaw resonant response, are elicited during shutdown. If the pitch system has a fault and one blade is hindered from normal pitching, the uneven load distribution of the blades leads to large structural and motion responses. For both turbines, the response maxima vary cyclically with the instantaneous azimuth when the blades start pitching to feather. For the floating wind turbine, the interaction of waves and wind also affects the results. The effect of the pitch rate during shutdown is analysed. The responses of the land‐based turbine in grid loss and shutdown conditions are proportional to the pitch rate, whereas decreased sensitivity is found in the cases with pitch system faults. For the floating turbine, the effect of the pitch rate is small, and reduced pitch and yaw motion extremes are observed as the pitch rate increases. Copyright © 2013 John Wiley & Sons, Ltd.     

Prediction of aerodynamic performance of NREL offshore 5-MW baseline wind turbine considering power loss at varying wind speeds

In this study, a computational fluid dynamics (CFD) model was developed to simulate the aerodynamic performance of the National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine with single rotor and full wind turbine. Using statistical methods, the relation between pitch angle and performance when the speed is above the rated wind speed was analyzed; furthermore, other published data were compiled to establish the functional equations of power, thrust with various inflow wind speeds, and pitch angles. In addition, according to shape optimization based on parametric modeling, the two-dimensional cross-section of the wind turbine blade can be defined through a metasurface approach, and the three-dimensional surface modeling of the wind turbine blade, nacelle, and tower is completed using the nonuniform rational B-splines (NURBS) interpolator. In terms of aerodynamic simulation, the unstructured polygon mesh was used herein to discretize the space and simulate the highly curved and twisted surfaces of the blade. In this study, the compact and accurate mesh form obtained through a grid independence test will be used to analyze the distribution of the pressure coefficient, shear stress coefficient, and limited streamline on the blade surface at various inflow wind speeds and pitch angles to understand the differences between different turbulence models and the causes of power and thrust attenuation at high inflow wind speeds. In addition, the phenomena of blade-tip vortices, dynamic stall, blade loading, and the interaction between nacelle and tower were collectively explored.     

不同冲角下汽轮机拉筋气动损失系数的计算

采用Fluent软件对装有圆柱拉筋的平面叶栅进行了数值模拟,主要研究了圆柱拉筋引起的平面叶栅气动性能的变化以及叶片冲角对装有圆柱拉筋的平面叶栅的影响,计算了不同冲角下拉筋引起的损失系数,并与前人所做的实验结果吻合较好。结果表明:拉筋促使吸力面的流动分离加剧,使得吸力面附近的流动异常复杂。关于拉筋中心线形成上、下一个高损失涡对,在该处气流欠偏转;而在这个涡对中间的流体马赫数较高,气流呈过偏转。