1,720,998 research outputs found
Performance enhancement of a vibration energy harvester via harmonic time-varying damping: A pseudospectral-based approach
Full text linkEnergy harvesting technologies are attracting increasing attention in the last decades, mainly thanks to the rapid advancement of sensors miniaturization, wireless sensors network, the internet of things, and the growing awareness on energy efficiency. The main objective of current research on energy harvesters is to enlarge the natural response bandwidth in order to increase the otherwise insufficient performance away from resonance. While popular approaches consider the inclusions of specific nonlinearities, this paper investigates the benefits of time variations of the damping coefficient of a linear power take-off system. A rigorous mathematical framework is firstly introduced, based on optimal control and pseudospectral decomposition, providing proofs and conditions for the existence of an unique optimal solution. Furthermore, a convenient algebraic formulation for the calculation of the steady-state response is provided, applicable to a wider family of time-varying systems. Such a tool is used to extensively study harmonic variations of the control damping parameters, discussing various combinations of orders and orthogonal terms. The optimization is first performed unconstrained, then forcing passivity, hence considering both active and semi-active controls. It is found that, in both cases, the best performance is achieved with damping variations at twice the exciting frequency, including both cosine and sine terms in the control law, while lower and higher harmonics are of less relevance
Tidal barrage operational optimisation using wave energy control techniques
Full text linkTidal barrages have been used as a source of renewable energy since Medieval times, though the commercial utilisation of tidal barrages for electricity production began in 1966. In the intervening time, a number of techniques have been used to optimise the operation of tidal barrages, in order to maximise their utility, against set criteria, usually including maximisation of converted energy. This paper examines what can be learned from a sister renewable energy application, wave energy, in terms of the energy-maximising control schemes employed. Specifically, comparisons are made in terms of the characteristics of the primary energy excitation, the set of control protocols available, and the mathematical models used to describe each system. In order to provide a preliminary assessment of the potential for the use of wave energy control concepts, a sample case study is undertaken, where a popular wave energy control philosophy is used to optimise the operation of a tidal barrage. Copyright (C) 2022 The Authors
A control design framework for wave energy devices
Full text linkThis paper presents an integrated framework for the design of wave energy control systems, considering the totality of the design process as well as any ancillary functions required, such as model reduction, excitation force estimation, etc. In particular, we propose the moment-based mathematical framework as an integrated environment which allows a smooth transition between modelling and control activities, as well as providing a framework to consider optimal rejection of modelling errors or errors in excitation force estimation. The paper provides an overview of the framework, also containing an illustrative case study to demonstrate a likely pathway through the framework
On the Effect of Wave Direction on Control and Performance of a Moored Pitching Wave Energy Conversion System
Full text linkIn the pathways towards the commercialisation of wave energy systems, the need for reliable mathematical models is of paramount importance for the design and synthesis of model-based control techniques to maximise the performance of wave energy converters (WECs). Furthermore, these offshore marine systems are held in position by the use of mooring systems, which have recently been analysed beyond survivability conditions to investigate their influence on control synthesis and device performance. In this study, we delve into the complex challenge of incorporating relevant mooring dynamics in defining a representative control action while also examining the influence of wave directionality on the overall procedure. For the specific case of a spread mooring system, where the hull cannot weathervane and operates based on directionality, control synthesis must be performed taking into account this characteristic of the resource. In this context, because it is able to harvest energy from only the bow-directed waves, the PeWEC is considered as a representative case study. The control synthesis is realised using a tailored data-based model, and device performance is evaluated across different site conditions while accounting for wave direction. Among our overall conclusions, we show that neglecting the directionality of the wave resource for the PeWEC case study can lead to an overestimation of device performance of up to (Formula presented.), even though a prevalent wave direction exists at the site
Time-varying damping coefficient to increase power extraction from a notional wave energy harvester
Full text linkEnergy efficiency and renewable energy generation is attracting increasing attention, due to the established understanding that a new sustainable approach to power human activities is compulsory, on the one hand, and thanks to technological advances, on the other hand. Energy harvesters, at different scales, are promising tools, but their performance and economic viability depend on advanced energy-maximisation control techniques. This paper borrows a control strategy from the vibration energy harvesting field, and implements it to a notional wave energy conversion application. A linear time variant damping coefficient of the power take-off unit is considered, oscillating at twice sinusoidal excitation force frequency, inducing parametric resonance in the system and significantly expanding the response bandwidth. Active and semi-active solutions are investigated, allowing or preventing bi-directional power flow, comparing results with traditional passive and impedance-matching control. Results show that, although both active and semi-active control successfully increase the mean power extraction, much larger than passive control, semi-active control ensures better power quality and lower control forces
Optimisation and control of tidal range power plants operation: Is there scope for further improvement?
Full text linkTidal barrage power plants utilise the tidal range variation to generate clean electricity. Although there are
several operating tidal barrage schemes around the globe, there is still potential to expand the installed capacity.
Given their inherent storage and the high predictability of the tides, tidal barrages can be operated with more
flexibility than many other renewables. This means that the control objective of a barrage operation can vary
from energy maximisation to constant power output, or demand-matching objectives. The operation of a barrage
also influences its impact on the environment and economic activity of the site where it is located, which is a
major cause for the slow deployment of such power plants. The aim of this study is to provide a comprehensive
and critical analysis of the different strategies considered to date to optimise the operation of tidal barrages, with
a focus on an in-depth analysis of the optimisation schemes employed, the barrage models utilised, and opportunities for further improvement
Flexible operation of tidal barrages for demand-matching generation: A case study in the La Rance power plant
No full textTidal barrage power plants use the difference in tidal elevation throughout the day to generate electrical power. The inner basin that these type of power plants have, combined with the slow variation of the tides, allow for an element of time-varying storage capacity compared to other more traditional renewable sources, such as wind and solar. This study focuses on exploiting the flexibility of tidal barrages to achieve a demand-following operation. Using the La Rance power plant as a case of study, and a typical residential demand curve, the optimal operation of a barrage is computed pursuing two different objectives: energy maximisation and demand matching. The resulting optimal control problem associated with each objective is solved using the moment-based control framework. Furthermore, a receding-horizon strategy is implemented, to account for the potential variability in the electrical demand, which presents a stochastic behaviour
Towards efficient control synthesis for nonlinear wave energy conversion systems: impedance-matching meets the spectral-domain
Full text linkExisting studies within the literature that focus on designing parametric energy-maximizing controllers for Wave Energy Converter (WEC) systems predominantly rely on the impedance-matching (IM) principle, originally developed for linear time-invariant systems. Alternatively, iterative optimization routines are commonly employed for nonlinear WECs. However, these approaches often face a trade-off between effectiveness in maximizing energy extraction and computational efficiency. To address this limitation, this study proposes a computationally efficient controller tuning method for analogous synthesis in the case of nonlinear WECs. The proposed approach combines a statistical linearization technique known as spectral-domain modeling with the IM principle, to synthesize a Proportional–Integrative (PI) controller for a nonlinear WEC. Furthermore, a comparison is performed with two other synthesis methods: one based on a standard (i.e. linear) frequency-domain representation of the WEC that incorporates the IM principle, and the other employing a gradient-free optimization routine applied to the nonlinear time-domain model of the WEC for PI parameter tuning through exhaustive numerical search. A discussion on the effectiveness of each tuning method in maximizing energy absorption is provided, including an appraisal of their associated computational time requirements. Numerical analyses demonstrate that the proposed method, which integrates spectral-domain modeling and IM, can achieve (almost) optimal PI controller design for a nonlinear WEC. Furthermore, this study addresses the inaccuracies inherent in the frequency-domain approach and significantly reduces the computational time compared to the exhaustive search procedure. The findings of this research represent a significant advancement towards the development of simple, effective, and efficient IM-based techniques for synthesis of controllers in nonlinear WEC system
Energy-maximising moment-based constrained optimal control of ocean wave energy farms
Full text linkSuccessful commercialisation of wave energy technology inherently incorporates the concept of an array of wave energy converters (WECs). These devices, which constantly interact via hydrodynamic effects, require optimised control that can guarantee maximum energy extraction from incoming ocean waves while ensuring, at the same time, that any physical limitations associated with device and actuator systems are being consistently respected. This paper presents a moment-based energy-maximising optimal control framework for WECs arrays subject to state and input constraints. The authors develop a framework under which the objective function (and system variables) can be mapped to a finite-dimensional tractable quadratic program (QP), which can be efficiently solved using state-of-the-art solvers. Moreover, the authors show that this QP is always concave, i.e. existence and uniqueness of a globally optimal solution is guaranteed under this moment-based framework. The performance of the proposed strategy is demonstrated through a case study, where (state and input constrained) energy-maximisation for a WEC farm composed of CorPower-like WEC devices is considered
Energy-maximising tracking control for a nonlinear heaving point absorber system commanded by second order sliding modes
Full text linkEnergy-maximising control has proven to be of fundamental aid in the pathway towards commercialisation of wave energy conversion technology. The WEC control problem is based upon the design of a suitable control law capable of maximising energy extraction from the wave resource, while effectively minimising any risk of component damage. A particularly well-established family of WEC controllers is based upon a composite structure, where an optimal velocity reference is generated via direct optimal control procedures, followed by a suitable tracking control strategy. This paper presents the design and synthesis of a second order sliding mode controller to attain a reference tracking for a wave energy system. The presented approach can inherently handle parameter uncertainty in the model, which is ubiquitous within hydrodynamic modelling procedures. Furthermore, the proposed sliding mode controller has relatively mild computational requirements, and finite-time convergence to the designed surface, hence being an ideal candidate for real-time energy-maximising control of WEC systems. Copyright (C) 2022 The Authors
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