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

这项建议将开发新型的被动减振技术，以抑制采用静液传动传动系的新型风力机浮动平台的振动，并发展具有非线性反馈的无限维耦合系统的稳定性理论。背景：为了获取最高质量的风能资源，风力机正随着浮动风力机技术在海上进一步部署。然而，与固定底部风力涡轮机相比，浮动风力涡轮机面临着来自天气和海浪条件的更严峻挑战。浮式平台的运动不仅会引起转子转速和发电机功率的大幅波动，而且还会引起塔基上的负荷波动。已知的减振方法是通过扭矩控制和叶片螺距控制。但这些方法是有效的，但代价是干扰发电，而后者将增加叶片变桨距执行器的使用。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)，可能是一种很好的替代解决方案。它们没有电气故障，但TMD/TLCD类型的阻尼器的一大缺点是它们的质量和/或大量的液体，导致大量额外的重量，这是可以防止的，如果他们利用现有的涡轮部件。然而，实际考虑表明，现有组件无法使用，因此对于常规风力涡轮机来说，这不是一个现实的解决方案。一种新型的风力机--静压传动风力机(HSTWT)，可以提供合适的质量和液体分量。控制应用：该项目将研究如何利用浮式驳船上安装的液压储液器作为一种新型阻尼器来抑制浮式平台的振动。这将以非常小的额外成本简单地给储水器提供双重功能。在项目期间，我们将利用国家可再生能源实验室开发的现有浮式风力发电机组的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-蓄水池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：上述塔架(包括驳船)-阻尼器系统是两个被动系统的互联。然而，这并不会自动带来稳定。我们将这个问题抽象为稳定性理论，并进一步研究：假设塔是柔性的，用偏微分方程组来描述，这样它就是一个无限维系统。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。工程中的耦合系统往往由无限维系统与有限维系统相互作用组成，即可用常微分方程组描述的系统。这类耦合系统是最近线性情形下的热门研究课题。非线性有限维系统的情况是开放和具有挑战性的。因此，发展无源线性无穷维系统与无源非线性有限维系统互联的稳定性理论将是非常有意义的。耦合系统的方程可改写为含非线性阻尼项的希尔伯特空间中的抽象二阶微分方程组。我们的目标是利用单调算子理论和Lyapunov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，所有这些都在PI的多学科背景下得到了很好的体现。

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.