Passive vibration control of a floating hydrostatic transmission wind turbine and theoretical extensions

摘要：本课题将开发一种新型的被动阻尼技术来抑制一种采用静压传动传动系统的新型风力发电机浮动平台的振动，并建立具有非线性反馈的耦合无限维系统的稳定性理论。背景：为了捕获最高质量的风力资源，风力涡轮机正随着浮动风力涡轮机技术被部署到更远的海上。然而，与固定底部的风力涡轮机相比，漂浮式风力涡轮机面临着来自天气和海浪条件的更严峻挑战。浮动平台的运动不仅会引起转子转速和发电机功率的较大波动，而且还会引起塔基上相当大的负荷变化。已知的减振方法有转矩控制和桨距控制。但这些方法都是以干扰发电为代价的，后者会增加桨距作动器的使用。结构控制，例如，使用调谐质量阻尼器（TMD）或调谐液柱阻尼器（TLCD），可能是一个很好的替代解决方案。它们没有电气故障，但TMD/TLCD型阻尼器的一大缺点是它们具有大质量和/或大量液体，导致大量额外的重量，如果它们使用现有的涡轮组件，这可以防止。然而，实际考虑表明，现有的组件不能使用，所以这不是一个现实的解决方案，传统的风力涡轮机。一种新型风力机——静压传动风力机（HSTWT）能够提供合适的质量和液体成分。控制应用：建议项目将研究如何利用安装了HSTWT的浮船的水力蓄水池，作为一种新型的阻尼器，来抑制浮动平台的振动。这将简单地使水库具有双重功能，而额外成本非常小。在项目中，我们将使用国家可再生能源实验室开发的现有浮式风力涡轮机仿真模型进行详细的仿真分析。该模型将进行修改，以包括HST动力传动系统、驳船-油藏系统的耦合动力学以及俯仰和扭矩控制器。阻尼器的优化设计将基于上述仿真模型通过系统辨识得到的两个简单模型和粒子群优化算法。控制理论：上述塔（包括驳船）-阻尼器系统是两个被动系统的互连。然而，这并不会自动导致稳定。我们将这个问题抽象为稳定性理论，并进一步考虑：假设塔是柔性的，用偏微分方程来描述，因此它是一个无限维系统。当两个系统在两个方向上相互影响时，它们被称为耦合系统。工程中的耦合系统通常由无限维系统与有限维系统相互作用组成，即可以用常微分方程描述的系统。在线性情况下，这种耦合系统是最近研究的热点。非线性有限维系统的情况是开放的和具有挑战性的。因此，发展无源线性无限维系统与无源非线性有限维系统互连的稳定性理论将是非常有趣的。耦合系统的方程可以重写为Hilbert空间中带有非线性阻尼项的抽象二阶微分方程。我们的目的是利用单调算子理论和李雅普诺夫函数来研究这类系统的稳定性。这项工作需要深入了解流体力学、结构动力学和控制理论与工程，这些都在PI的多学科背景中得到了很好的体现。

Short summary:This proposal will develop novel passive damping technology to dampen the vibrations of the floating platform of a new type of wind turbine employing the hydrostatic transmission drivetrain, and develop a stability theory for coupled infinite-dimensional systems with nonlinear feedback.Background:In order to capture the highest quality wind resources, wind turbines are getting deployed further offshore with the floating wind turbine technology. However the floating wind turbines face more severe challenges from weather and wave conditions than their fixed-bottom counterparts. The motions of the floating platform not only cause large fluctuations in the rotor speed and generator power, but also cause considerable load variations on the tower base. Known vibration reduction methods are by torque control and by blade pitch control. But these methods are effective at the expense of interfering with the power generation and the latter will increase blade pitch actuator usage. Structural control, e.g., using tuned mass damper (TMD) or tuned liquid column damper (TLCD), might offer a good alternative solution. They are free from electrical faults, but a big disadvantage of TMD/TLCD type of dampers is that they have a large mass and/or a large amount of liquid, leading to substantial extra weight, this could be prevented if they made use of existing turbine components. However, practical considerations have shown that existing components cannot be used, so this is not a realistic solution for conventional wind turbines. A new type of wind turbine called hydrostatic transmission wind turbine (HSTWT), could provide the suitable mass and liquid component.Control Application:The proposed project will investigate how to make use of the hydraulic reservoir of the floating barge mounted HSTWT to dampen the vibrations of the floating platform, by acting as a novel damper. This will simply give the reservoir a dual function with very small extra costs. During the project we will use existing simulation model of the floating wind turbines developed by the National Renewable Energy Laboratory for detailed simulation analysis. This model will be modified to include the HST drivetrain, coupled dynamics of the barge-reservoir system, and pitch and torque controllers. The optimal damper design will be based on two simple models obtained from the above simulation model through system identification, and Particle Swarm Optimization algorithm. Control theory: The above tower (including the barge) - damper system is the interconnection of two passive systems. However this does not automatically lead to stability. We abstract this problem as stability theory and look even further: assuming the tower is flexible, which is described by partial differential equations, so that it is an infinite-dimensional system. When two systems influence each other in both directions, they are known as a coupled system. Coupled systems in engineering often consist of an infinite-dimension system interacting with a finite-dimensional system, i.e., a system that can be described by ordinary differential equations. Such coupled systems have been recently the topic of intense research in the linear case. The case of a nonlinear finite-dimensional system is open and challenging. Thus it will be very interesting to develop a stability theory for the interconnection of a passive linear infinite-dimensional system and a passive nonlinear finite-dimensional system. The equations of the coupled system can be rewritten as an abstract second order differential equation in a Hilbert space, with a nonlinear damping term. We aim to investigate the stability properties of such systems using monotone operator theory and Lyapunov functions.This work requires an in-depth understanding of fluid mechanics, structural dynamics and control theory and engineering, all of which are well represented in the PI's multi-disciplinary background.