Vibration and power regulation control of a floating wind turbine with hydrostatic transmission

We design a blade pitch controller employing linear parameter-varying (LPV) synthesis techniques for a floating hydrostatic wind turbine (HWT) with a barge platform, which is based on the LIDAR (Light Detection and Ranging) preview on the wind speed. The developed control system can simultaneously reduce barge pitch motions and regulate the power in Region 3. These two functions would normally disturb each other if designed separately. The state space model is not affinely dependent on the wind speed thus the LPV controller is obtained by satisfying multiple LMIs evaluated at a set of gridded points within the wind speed range in Region 3. An anti-windup compensation scheme is then used to improve the LPV controller’s performance when the pitch undergoes saturation around the rated wind speed. The simulations based on a high-fidelity barge HWT model show that our pitch controller significantly reduces barge pitch motions, loads on blade bearings & tower, and generator power fluctuations, compared with a gain-scheduled PI pitch controller

Fault estimation and fault-tolerant control for discrete-time dynamic systems

In this paper, a novel discrete-time estimator is proposed, which is employed for simultaneous estimation of system states, and actuator/sensor faults in a discrete-time dynamic system. The existence of the discrete-time simultaneous estimator is proven mathematically. The systematic design procedure for the derivative and proportional observer gains is addressed, enabling the estimation error dynamics to be internally proper and stable, and robust against the effects from the process disturbances, measurement noise, and faults. Based on the estimated fault signals and system states, a discrete-time fault-tolerant design approach is addressed, by which the system may recover the system performance when actuator/sensor faults occur. Finally, the proposed integrated discrete-time fault estimation and fault-tolerant control technique is applied to the vehicle lateral dynamics, which demonstrates the effectiveness of the developed techniques

Control of Ocean Wave Energy Converters with Finite Stroke

In the design of ocean wave energy converters, proper control design is essential for the maximization of power generation performance. However, in practical applications, this control must be undertaken in the presence of stroke saturation and model uncertainty. In this dissertation, we address these challenges separately. To address stroke saturation, a nonlinear control design procedure is proposed, which guarantees to keep the stroke within its limits. The technique exploits the passivity of the wave energy converter to guarantee closed-loop stability. The proposed technique consists of three steps: 1) design of a linear feedback controller using multi-objective optimization techniques; 2) augmentation of this design with an extra input channel that adheres to a closed-loop passivity condition; and 3) design of an outer, nonlinear passive feedback loop that controls this augmented input in such a way as to ensure stroke limits are maintained. The discrete-time version of this technique is also presented. To address model uncertainty, in particular we consider the nonlinear viscosity drag effect as the model uncertainty. This robust control design problem can be regarded as a multi-objective optimization problem, whose primary objective is to optimize the nominal performance, while the second objective is to robustly stabilize the closed-loop system. The robust stability constraint can be posed using the concept of circle criterion. Because this optimization is non-convex, Loop Transfer Recovery methods are used to solve for sub-optimal solutions to the problem. These techniques are demonstrated in simulation, for arrays of buoy-type wave energy converters.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163263/1/waynelao_1.pd

Structural Control Strategies for Load Reduction of Floating Wind Turbines

Doktorgradsavhandling ved Fakultet for Teknologi og realfag, Universitetet i Agder, 2015Offshore wind energy has attracted great worldwide attention in recent years, while strong potentials have been found in deep sea areas in many places, such as the coastal lines of the United States, north Europe, and east Asia. According to extensive experiences in offshore industry, floating foundation for wind turbines is considered as an economical and applicable solution. So far, plenty of numerical investigations have been conducted by world-wide research institutions, and different kinds of prototype programs have also been launched, including OC3-Hywind, MIT/NREL TLP, ITI Barge, and Principle Power WindFloat, etc. One big challenge for floating windmills different from fixed bottom installations is the extra platform motion, which will heavily increase the load on turbine structure due to the high inertial and gravitational forces or even cause the failure of turbine control strategy. Special mechanical design or advanced control technique is required to improve wind turbine reliability, and effective load reduction methods are needed for the design of floating wind turbines. Among different approaches for load mitigation, structural control has offered a direct solution to dynamically compensate the vibrations of turbine structures and reduce their loads. This dissertation is mainly about the numerical investigations of different structural control ideas for load reduction of floating wind turbines. The state-of-the-art wind turbine simulator FAST-SC (customized for structural control analysis) is used in the simulation analysis, and different scenarios, including the below rated, rated, and parked situations, are considered respectively. Papers A and B are dealing with the parameter optimization problem of a spar-type floating wind turbine equipped with tuned mass dampers (TMDs). The passive structural control devices can either be installed inside the platform (Paper A) or along the nacelle (Paper B). Different performance indices and parameter optimization methods are adopted for TMD parameter determination, including frequency analysis, exhaustive search, and intelligent algorithms. Particularly, a mathematical model for wind turbine surge-heavepitch motion is established based on the D’Alembert’s principle of inertial forces. Paper C investigates the idea of installing tuned liquid column dampers (TLCDs) in floating wind turbines for load reduction, and the code FAST-SCTLCD is implemented based on FAST-SC for fully coupled high-fidelity wind turbine simulation with semi-active structural control channel. Optimal parameters are computed by using genetic algorithm based on the established model, while how to tune the head loss coefficient remains to be investigated. Paper D proposes a gain scheduling H2/H∞ active structural control deign for a hybrid mass damper (HMD) installed at the tower top of a floating wind turbine. The wind turbine dynamic model is improved in this work based on polynomial curve fitting approach, and different steady-state points are derived. The state feedback controller is designed by solving linear matrix inequalities (LMIs). However, full-state feedback controller is technically impossible to implement due to lack of sensors, while the observer-based control design could be a possible solution. Then, Paper E discusses this idea, and an observer-based guaranteed cost structural controller is developed

Advanced control designs for output tracking of hydrostatic transmissions

The work addresses simple but efficient model descriptions in a combination with advanced control and estimation approaches to achieve an accurate tracking of the desired trajectories. The proposed control designs are capable of fully exploiting the wide operation range of HSTs within the system configuration limits. A new trajectory planning scheme for the output tracking that uses both the primary and secondary control inputs was developed. Simple models or even purely data-driven models are envisaged and deployed to develop several advanced control approaches for HST systems

Control of large offshore wind turbines.

Several control strategies are proposed to improve overall performances of conventional (geared equipped) and hydrostatic offshore wind turbines. Firstly, to maximise energy capture of a conventional turbine, an adaptive torque control technique is proposed through simplifying the conventional extremum seeking control algorithm. Simulations are conducted on the popular National Renewable Energy Laboratory (NREL) monopile 5-MW baseline turbine. The results demonstrate that the simplified ESC algorithms are quite effective in maximising power generation. Secondly, a TMD (tuned mass damper) system is configured to mitigate loads on a monopile turbine tower whose vibrations are typically dominated by its first mode. TMD parameters are obtained via H2 optimisation based on a spatially discretised tower-TMD model. The optimal TMDs are assessed through simulations using the NREL monopile 5-MW baseline model and achieve substantial tower load reductions. In some cases it is necessary to damp tower vibrations induced by multiple modes and it is well-known that a single TMD is lack of robustness. Thus a control strategy is developed to suppress wind turbine’s vibrations (due to multiple modes) using multiple groups of TMDs. The simulation studies demonstrate the superiority of the proposed methods over traditional ones. Thirdly, the NREL 5-MW baseline turbine model is transformed into a hydrostatic wind turbine (HWT). An H∞ loop-shaping torque controller and a light detection and ranging-based linear-parameter-varying anti-windup pitch controller are designed for the HWT. The tests on a monopile HWT model indicate good tracking behaviours of the torque controller and much improved performances of the linear-parameter-varying pitch controller over a gain-scheduled PI pitch controller. Finally, the hydraulic reservoir of a barge HWT is made into a bidirectional-tuned- liquid-column-damper (BTLCD) to suppress barge pitch and roll motions. The simulation results validate the effectiveness of the optimal BTLCD reservoir in reducing the tower loads and power fluctuations

Wind Turbine Reliability Improvement by Fault Tolerant Control

This thesis investigates wind turbine reliability improvement, utilizing model-based fault tolerant control, so that the wind turbine continues to operate satisfactorily with the same performance index in the presence of faults as in fault-free situations. Numerical simulations are conducted on the wind turbine bench mark model associated with the considered faults and comparison is made between the performance of the proposed controllers and industrial controllers illustrating the superiority of the proposed ones

Aeronautical engineering: A continuing bibliography with indexes, supplement 100

This bibliography lists 295 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System in August 1978

Bibliography of Lewis Research Center technical publications announced in 1986

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1986. All the publications were announced in the 1986 issues of Scientific and Technical Aerospace Reports (STAR) and/or International Aerospace Abstracts (IAA). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses