Nonlinear Control and Estimation of a Tethered Kite in Changing Wind Conditions
Nonlinear Control and Estimation of a Tethered Kite in Changing Wind Conditions
复制标题
风况变化时系留风筝的非线性控制与估计
DOI：
10.2514/1.31604
复制
发表时间：
2008
影响因子：
2.6
通讯作者：
W. Ockels
中科院分区：
文献类型：
--
作者：
P. Williams;B. Lansdorp;W. Ockels
K ITE 系统已被认为是利用高空风发电的潜在手段[1-3]。许多从高海拔地区提取风能的早期概念都集中在将发电机放置在盛行风中[4,5]。这样做的主要缺点是为了将系统维持在所需的高度而浪费大量的电力。或者，将发电机保持在地面上并使用轻型提升体在电缆中产生张力，可以将风能转化为机械功。这种思路激发了人们对系绳风筝的浓厚兴趣，因为测试不同概念相对容易。目前针对基于风能机械传输的发电提出了两种主要设计概念：1）通过交替电缆长度驱动的水平轴发电机和2）通过系绳张力产生的扭矩驱动的垂直轴发电机。第一个概念控制提升体的运动，使得在缆绳放出期间产生高张力，而在卷绕阶段产生低张力。张力的差异可以产生净功率。垂直轴概念要求以最大化发电机扭矩的方式放风筝。这两个概念都要求可以控制风筝使其飞行合适的轨迹。为了使风筝发电成为现实，有必要实现一个能够以稳健的方式自主控制风筝系统的控制系统。目前，该领域的研究因缺乏足够的数据来构建准确的风筝模型而受到限制。最近的工作重点是提取实验数据以帮助模型识别和模型开发[6]。在[7]中，使用了风筝的多板表示，允许通过风筝上系绳附着点的移动进行控制。然而，从控制工程师的角度来看，大多数风筝系统的高度灵活性使得建模成为一个挑战。使用流固耦合方法可以开发高度详细的模型，但这些模型速度太慢，无法实现控制系统的开发。这项工作建立在[3]中提出的工作的基础上，该工作详细介绍了风筝系统的非线性最佳发电轨迹的设计。本文旨在开发一种用于操纵系留风筝轨迹的初步控制系统。我们通过仅考虑系统产生的力，采用非常简单的风筝动力学近似。目标是创建一种方法，在不同的风力条件下稳定风筝围绕一组特定参考轨迹的运动。在实际系统中，风速一般是未知的，并且风速在大小和方向上都会波动。控制系统必须能够处理风速和风向的变化。在本笔记中，我们描述了非线性反馈控制器的开发，该控制器使用系统的一组噪声测量来稳定风筝运动。数值模拟用于证明控制器跟踪发电轨迹的有效性。这项工作表明，可以使用不精确的反馈和具有代表性的系绳动态模型的非线性最优控制来闭合风筝的环路。
K ITE systems have been identified as a potential means for generating power from high-altitude winds [1–3]. Many early concepts for extracting wind energy from high altitudes focused on placing a generator in the prevalent winds [4,5]. This has the major drawback of wasting a significant amount of power just to maintain the system at the desired altitude. Alternatively, keeping the generator on the ground and using a light lifting body to generate tension in the cable allows converting the wind energy into mechanical work. This line of thinking has stimulated a lot of interest in tethered kites because of the relative ease with which different concepts can be tested. There are currently two major design concepts that have been suggested for power generation based onmechanical transmission of the wind energy: 1) horizontal-axis generators that are driven by alternating the cable length and 2) vertical-axis generators that are driven by a torque created by the tether tension. The first concept controls themotion of the lifting body in such away that high tension is created during payout of the cable and low tension is generated during the reel-in phase. The difference in tension allows net power to be generated. The vertical-axis concept requires flying the kite in a way that maximizes the torque on the generator. Both of these concepts require that the kite can be controlled to fly suitable trajectories. Tomake power generation through kites a reality, it is necessary to implement a control system that can autonomously control the kite system in a robust manner. Currently, research in this area is limited by the unavailability of sufficient data to allow accurate kite models to be constructed. Recent work has focused on the extraction of experimental data to help model identification and model development [6]. In [7], a multiplate representation of the kite was used that allowed for control by movement of the tether attachment points on the kite. However, the high flexibility of most kite systems makes modeling a challenge when viewed from a control engineer’s perspective. Highly detailed models can be developed using fluid– structure interaction methodologies, but these would be too slow to enable control system development. This work builds on the work presented in [3],which details the design of nonlinear optimal powergenerating trajectories for kite systems. This paper is aimed at developing a preliminary control system for manipulating the trajectory of a tethered kite. We employ a very simple approximation of the kite dynamics by considering only the forces generated by the system. The goal is to create a means for stabilizing the kite motion around a particular set of reference trajectories under varying wind conditions. In a practical system, the wind speed is not known in general, and it fluctuates in both magnitude and direction. The control system must be capable of handling changes in wind speed and direction. In this Note, we describe the development of a nonlinear feedback controller that stabilizes the kite motion using a set of noisy measurements of the system. Numerical simulations are used to demonstrate the effectiveness of the controller for tracking power-generation trajectories. This work shows that the loop can be closedwith the kite using inexact feedback and nonlinear optimal control with a representative tether dynamic model.