Control design for a two-bladed downwind teeterless damped free-yaw wind turbine

In this paper, a control architecture for a two-bladed downwind teeterless damped free-yaw wind turbine is developed. The wind turbine features a physical yaw damper which provides damping to the yawing motion of the rotor-nacelle assembly. Individual Pitch Control (IPC)¹ is employed to obtain yaw control so as to actively track the wind direction and to reduce the turbine loads. The objectives of both load and yaw control by IPC are conflicting and therefore two decoupling strategies are presented and compared in terms of controller design, stability, and turbine loads. The design of the different controllers and the physical yaw damping are coupled and have a large impact on the turbine loads. It is shown that the tuning of the controllers and the choice of the yaw damping value involve a tradeoff between blade and tower loads. All results have been obtained by high-fidelity simulations of the state-of-the-art 2-B Energy 2B6 wind turbine.     

Performance analysis of individual blade pitch control of offshore wind turbines on two floating platforms

Individual blade pitch state space (IBP SS) control and disturbance accommodating control (DAC) that reject wind speed perturbations are applied on a 5 MW wind turbine mounted on the barge and tension leg floating platforms for performance comparison in above rated wind speed region. The DAC used in this study is simply an IBP SS controller with a wind speed disturbance rejection component. For each controller implemented onshore and on the floating platforms, 60 10-min simulations with a variety of wind and wave conditions, where applicable, are carried out in accordance with the IEC-61400-3 standard design load case 1.2 for fatigue load testing. Results show that even with large tower load reductions by the IBP SS controller on the barge platform, these loads are still at least two and up to five times more than that for an onshore wind turbine. DAC on the barge platform has little impact on further improving the performance of the IBP SS controller. DAC on the tension leg platform manages to achieve loads comparable to that of the onshore system. Power and rotor speed regulation are improved and tower side-side load is reduced. Only the tower fore-aft load is 24% higher than the onshore wind turbine.     

Performance of disturbance augmented control design in turbulent wind conditions

This paper investigates the use of disturbance models in the design of wind turbine individual pitch controllers. Previous work has used individual pitch control and disturbance models with the Multiblade Coordinate Transformation to design controllers that reduce the blade loads at the frequencies associated with the rotor speed. This paper takes a similar approach of using a disturbance model within the H_∞ design framework to account for periodic loading effects. The controller is compared with a baseline design that does not include the periodic disturbance model. In constant wind speeds, the disturbance model design is significantly better than the baseline design at canceling blade loads at the rotor frequencies. However, these load reduction improvements become negligible even under low turbulent wind conditions. The two controllers perform similarly in turbulent wind conditions because disturbance augmentation improves load reduction only at the multiples of the rotor frequency in the yaw and tilt moment channels whereas turbulence creates strong collective bending moments. In addition, turbulent wind contains energy across a broad frequency spectrum and improvements at multiples of the rotor frequency are less important in these conditions. Therefore inclusion of periodic disturbance models in the control design may not lead to the expected load reduction in fielded wind turbines.     

Innovative adaptive pitch control for small wind turbine fatigue load reduction

As a renewable source of energy, wind is widely used to produce electrical power. The progress of wind turbine technology can greatly benefit from the improvement of control algorithms. The pitch angle control of a horizontal axis wind turbine above the rated wind speed is a challenging issue related to the nonlinear aerodynamic behavior of blades. The linearization of aerodynamic model around nominal operating condition, as well as manufacturing deficiencies, result in unknown parameter uncertainties in a wind turbine model. Therefore, the performance of controller, which is designed based on the mathematical model, defects in practice. In the current paper, an adaptive self-tuning regulator (STR) configuration is proposed for the pitch control, so that the parameters of wind turbine model are constantly estimated and the controller gains are updated based on the assessed parameters. The STR structure consists of a recursive least square estimator and a proportional-integral-derivative (PID) controller with adjustable gains, which are determined by the pole placement method in a real-time routine. The robustness of the closed loop system is investigated by implementation of the control structure on an aero-servo-elastic wind turbine simulator. For the sake of comparison, a baseline gain scheduling PID controller, which is well-accepted for wind turbine pitch control, is designed. A comparison between the simulations of two controllers confirms a significant improvement in the closed-loop performance including less fluctuation of rotor speed and power besides minor fatigue loads on the blades and main-shaft.     

A novel pitch control system for a wind turbine driven by a variable-speed pump-controlled hydraulic servo system

The paper aims to develop a novel pitch control system for a large wind turbine driven by a variable-speed pump-controlled hydraulic servo system. To perform practical pitch control experiments, a full-scale test rig of the hydraulic pitch control system for a 2 MW wind turbine’s blade, including a novel pitch control mechanism, a variable-speed pump-controlled hydraulic servo system, a disturbance system and a PC-based control system, is designed and set up. The variable-speed pump-controlled hydraulic servo system, containing an AC servo motor, a constant displacement hydraulic piston pump two differential hydraulic cylinders and hydraulic circuits, achieved high response and high energy efficiency, so it is suitable for wind turbine applications. Besides, to implement the pitch control in the proposed novel pitch control system, an adaptive fuzzy controller with self-tuning fuzzy sliding-mode compensation (AFC-STFSMC) is developed to design the pitch controller. Finally, the developed variable-speed pump-controlled hydraulic servo system was built and verified for the path tracking control and path-positioning control of the pitch control of the wind turbines by practical experiments in a full-scale test rig under different path profiles, load torques, and random wind speeds.     

Adding feedforward blade pitch control to standard feedback controllers for load mitigation in wind turbines

Combined feedback/feedforward blade pitch control is compared to industry standard feedback control when simulated in realistic turbulent winds. The feedforward controllers are designed to reduce fatigue loads, increasing turbine lifetime and therefore reducing the cost of energy. Two feedforward designs are studied: collective-pitch model-inverse feedforward using a non-causal series expansion and individual-pitch gain-scheduled shaped compensator. The input to the feedforward controller is a measurement of incoming wind speed, which could potentially be provided by LIDAR. Three of the designs reduce structural loading compared to standard feedback control, without reducing power production.     

Generator speed regulation in the presence of structural modes through adaptive control using residual mode filters

Wind turbines operate in highly turbulent environments resulting in aerodynamic loads that can easily excite turbine structural modes, potentially causing component fatigue and failure. Two key technology drivers for turbine manufacturers are increasing turbine up time and reducing maintenance costs. Since the trend in wind turbine design is towards larger, more flexible turbines with lower frequency structural modes, manufacturers will want to develop control paradigms that properly account for the presence of these modes. Accurate models of the dynamic characteristics of new wind turbines are often not available due to the complexity and expense of the modeling task, making wind turbines ideally suited to adaptive control approaches. In this paper, we develop theory for adaptive control with rejection of disturbances in the presence of modes that inhibit the controller. A residual mode filter is introduced to accommodate these modes and restore important properties to the adaptively controlled plant. This theory is then applied to design an adaptive collective pitch controller for a high-fidelity simulation of a utility-scale, variable-speed wind turbine. The adaptive pitch controller is compared in simulations with a baseline classical proportional integrator (PI) collective pitch controller.     

Structural control of floating wind turbines

The application of control techniques to offshore wind turbines has the potential to significantly improve the structural response, and thus reliability, of these systems. Passive and active control is investigated for a floating barge-type wind turbine. Optimal passive parameters are determined using a parametric investigation for a tuned mass damper system. A limited degree of freedom model is identified with synthetic data and used to design a family of controllers using H_∞ multivariable loop shaping. The controllers in this family are then implemented in full degree of freedom time domain simulations. The performance of the passive and active control is quantified using the reduction in fatigue loads of the tower base bending moment. The performance is calculated as a function of active power consumption and the stroke of the actuator. The results are compared to the baseline and optimal passive system, and the additional achievable load reduction using active control is quantified. It is shown that the optimized passive system results in tower fore-aft fatigue load reductions of approximately 10% compared to a baseline turbine. For the active control, load reductions of 30% or more are achievable, at the expense of active power and large strokes. Active control is shown to be an effective means of reducing structural loads, and the costs in power and stroke to achieve these reductions are demonstrated.     

Controller design for a wind farm, considering both power and load aspects

In this paper, a wind farm controller is developed that distributes power references among wind turbines while it reduces their structural loads. The proposed controller is based on a spatially discrete model of the farm, which delivers an approximation of wind speed in the vicinity of each wind turbine. The control algorithm determines the reference signals for each individual wind turbine controller in two scenarios based on low and high wind speed. In low wind speed, the reference signals for rotor speed are adjusted, taking the trade-off between power maximization and load minimization into account. In high wind speed, the power and pitch reference signals are determined while structural loads are minimized. To the best of authors’ knowledge, the proposed dynamical model is a suitable framework for control, since it provides a dynamic structure for behavior of the flow in wind farms. Moreover, the controller has been proven exceptionally useful in solving the problem of both power and load optimization on the basis of this model.     

The use of preview wind measurements for blade pitch control

Light detection and ranging systems are able to measure conditions at a distance in front of wind turbines and are therefore suited to providing preview information of wind disturbances before they impact the turbine blades. In this study, preview-based disturbance feedforward control is investigated for load mitigation. Performance is evaluated assuming highly idealized wind measurements that rotate with the blades and compared to performance using more realistic stationary measurements. The results obtained using idealized, “best case” measurements show that excellent performance gains are possible with reasonable pitch rates. However, the results using more realistic wind measurements show that without further optimization of the controller and/or better processing of measurements, errors in determining the shear local to each blade can remove any advantage obtained by using preview-based feedforward techniques.     

Solid State Voltage and Frequency Controller for a Stand Alone Wind Power Generating System

This paper deals with the voltage and frequency controller of a wind turbine driven isolated asynchronous generator. The proposed voltage and frequency controller consists of an insulated gate bipolar junction transistor based voltage source converter along-with battery energy storage system at its dc link. The proposed controller is having bidirectional active and reactive powers flow capability by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind turbine. It is also having capability of harmonic elimination and load balancing. The proposed electro-mechanical system along with its controller is modeled and simulated in MATLAB using Simulink and power system block-set toolboxes. Performance of the proposed controller is presented to demonstrate voltage and frequency control of a wind turbine driven isolated asynchronous generator along with harmonic elimination and load balancing.     

Subspace predictive repetitive control to mitigate periodic loads on large scale wind turbines

Manufacturing and maintenance costs arising out of wind turbine dynamic loading are one of the largest bottlenecks in the roll-out of wind energy. Individual Pitch Control (IPC) is being researched for cost reduction through load alleviation; it poses a challenging mechatronic problem due to its multi-input, multi-output (MIMO) nature and actuation constraints related to the wear of pitch bearings. To address these issues, Subspace Predictive Repetitive Control (SPRC), a novel repetitive control strategy based on the subspace identification paradigm, is presented. First, the Markov parameters of the system are identified online in a recursive manner. These parameters are used to build up the lifted matrices needed to predict the output over the next period. From these matrices an adaptive repetitive control law is derived. To account for actuator limitations, the known shape of wind-induced disturbances is exploited to perform repetitive control in a reduced-dimension basis function subspace. The SPRC methodology is implemented on a high-fidelity numerical aeroelastic environment for wind turbines. Load reductions are achieved similar to those obtained with classical IPC approaches, while considerably limiting the frequency content of the actuator signals.     

基于压电材料的钢筋砼-钢组合塔筒损伤监测

钢筋混凝土-钢组合塔筒作为一种新型的风电塔架形式,其混凝土段的开裂对其使用寿命具有重要影响,对其混凝土段的开裂进行监测具有重要意义。该文提出了一种基于压电陶瓷激励的应力波测量的钢筋混凝土塔段的开裂监测方法,以某钢筋混凝土-钢塔筒缩尺模型为对象,以布置在钢筋混凝土塔筒表面的压电陶瓷片为激励器,利用布置在钢筋混凝土塔筒不同高度位置的压电陶瓷片作为传感器,实现在不同水平往复加载下的应力波的测量。对混凝土塔段从裂缝开始出现直至构件最终破坏整个过程各压电陶瓷片的响应进行分析,并定义损伤指标。结果表明,定义的指标不仅可较好反应裂缝实际出现位置,且与加载等级相关,所提出的监测方法可对钢筋混凝土塔段裂缝的发生和发展过程进行有效监测。     

Robust and fault-tolerant linear parameter-varying control of wind turbines

High performance and reliability are required for wind turbines to be competitive within the energy market. To capture their nonlinear behavior, wind turbines are often modeled using parameter-varying models. In this paper we design and compare multiple linear parameter-varying (LPV) controllers, designed using a proposed method that allows the inclusion of both faults and uncertainties in the LPV controller design. We specifically consider a 4.8 MW, variable-speed, variable-pitch wind turbine model with a fault in the pitch system.We propose the design of a nominal controller (NC), handling the parameter variations along the nominal operating trajectory caused by nonlinear aerodynamics. To accommodate the fault in the pitch system, an active fault-tolerant controller (AFTC) and a passive fault-tolerant controller (PFTC) are designed. In addition to the nominal LPV controller, we also propose a robust controller (RC). This controller is able to take into account model uncertainties in the aerodynamic model.The controllers are based on output feedback and are scheduled on an estimated wind speed to manage the parameter-varying nature of the model. Furthermore, the AFTC relies on information from a fault diagnosis system.The optimization problems involved in designing the PFTC and RC are based on solving bilinear matrix inequalities (BMIs) instead of linear matrix inequalities (LMIs) due to unmeasured parameter variations. Consequently, they are more difficult to solve. The paper presents a procedure, where the BMIs are rewritten into two necessary LMI conditions, which are solved using a two-step procedure.Simulation results show the performance of the LPV controllers to be superior to that of a reference controller designed based on classical principles.     

永磁直驱式变桨距风力发电机组的建模与控制

根据机组在高风速区和低风速区的特点,设计了变桨距控制系统,使得机组能够在低风速区实现最大风能跟踪。为了增强机组在复杂条件下运行特性,在高风速区采用了PID控制器。建立了机组的仿真模型,对不同风速下的机组的稳态和动态特性进行了仿真分析。仿真结果验证了采用方案和控制策略的可行性。     

用于风力发电机偏航控制的激光测风系统设计与试验

为实现风力发电机迎风信息的精确测量,采用连续波相干探测技术,设计了针对风力发电机偏航控制需求的激光测风系统。该系统的扫描装置中由直驱电机带动15°顶角楔形镜旋转实现激光对大气的圆锥扫描,设置扫描一圈用时为15 s,每圈采样点数为30个,利用正弦拟合方法反演风力发电机前方的风场信息。将激光测风系统安装在深圳市气象观测梯度塔下,与塔上超声波风速仪进行了对比测风试验。经过数据分析,水平风速相关系数达0.98,标准差为0.22 m/s,风向相关系数达0.97,标准差为3.04°,表明所设计的激光测风系统性能优良,工作稳定可靠,能够为风力发电机提供精确风场参数,提高风能的利用效率。     

风轮机叶片电磁散射特性的占比分析与解析模型的建立

针对风轮机叶片雷达散射截面积的变化特性,分析了风轮机叶片雷达散射截面积（Radar Cross Section, RCS）对其整体雷达散射特性占比情况,实现对叶片解析模型适用范围的选取。考虑了风轮机叶片旋转平面与雷达视线（Line of Sight, LOS）夹角、叶片材料、叶片几何形状等因素对风轮机散射特性的影响,运用UG软件对风轮机叶片进行三维建模,利用真实叶片与相应简化圆柱叶片电磁散射特性的差异构建高保真的风轮机真实叶片电磁散射特性的解析模型,实现风轮机叶片RCS的快速计算。最后将解析模型计算结果与实测数据进行对比,验证了论文给出的真实叶片电磁散射特性解析模型的有效性。      

Robust Yaw Stability Controller Design and Hardware-in-the-Loop Testing for a Road Vehicle

Unsymmetrical loading on a car like $mu$-split braking, side wind forces, or unilateral loss of tire pressure results in unexpected yaw disturbances that require yaw stabilization either by the driver or by an automatic driver-assist system. The use of two-degrees-of-freedom control architecture known as the model regulator is investigated here as a robust steering controller for such yaw stabilization tasks in a driver-assist system. The yaw stability-enhancing steering controller is designed in the parameter space to satisfy a frequency-domain mixed sensitivity constraint. To evaluate the resulting controller design, a real-time hardware-in-the-loop simulator is developed. Steering tests with and without the controller in this hardware-in-the-loop setup allow the driver to see the effect of the proposed controller to improve vehicle-handling quality. The hardware-in-the-loop simulation setup can also be used for real-time driver-in-the-loop simulation of other vehicle control systems.      

基于单–双高斯模型拟合法的测风激光雷达海上风电机组尾流特征分析

当气流经过风电机组的扫风平面时, 风电机组下风处产生的尾流效应会对风电机组的发电效率、疲劳载荷产 生不同程度的影响。基于相干多普勒测风激光雷达在江苏某海上风电场开展了全天候风场观测实验。由于紧邻风电 机组的尾流垂直截面上风速呈双高斯分布规律, 利用传统单高斯拟合算法存在计算误差较大, 无法反映真实流场风速 变化规律, 提出了一种单–双高斯模型拟合改进算法, 分析了目标风电机组尾流的尾流宽度、风速损失率和尾流长度 等参数特征, 研究结果验证了单–双高斯拟合算法对尾流横向风速拟合的可行性和准确性。     

基于改进时域高通滤波红外图像的海上风机塔架腐蚀速率预测北大核心CSCD

为提高海上风机塔架腐蚀速率预测精度与效率,提出基于改进时域高通滤波红外图像的海上风机塔架腐蚀速率预测方法。由基于改进时域高通滤波算法的塔架红外图像质量优化方法,在校正图像不同频域信息的偏移系数之上,引入减底图法、锐化滤波器,有效去除图像噪声信息,并增强塔架目标细节特征,从而优化图像质量;针对处理后塔架红外图像,经基于改进Niblack算法与最大熵算法的塔架红外图像分割方法,以背景、目标分离方式,提取塔架目标图像,作为基于天牛须搜索算法的极限学习机腐蚀速率预测方法的预测样本,预测海上风机塔架腐蚀速率。实验结果显示:该方法在迭代10次后便可高精度预测海上风机塔架腐蚀速率,具备海上风机塔架腐蚀速率准确、快速预测能力。