CLOSED LOOP ENERGY MAXIMIZING CONTROL OF A WAVE ENERGY CONVERTER USING AN ESTIMATED LINEAR MODEL THAT APPROXIMATES THE NONLINEAR FROUDE-KRYLOV FORCE

Wave energy converters (WECs) exploit ocean wave energy and convert it into useful forms such as electricity. But for WECs to be successful on a large scale, two primary conditions need to be satisfied. The energy generated must satisfy the network requirements, and second, energy flow from waves to the grid needs to be maximized. In this dissertation, we address the second problem. Most control techniques for WECs today use the Cummins\u27 linear model to simulate WEC hydrodynamics. However, it has been shown that under the application of a control force, where WEC motions are amplified, the linear model diverges from actual motions. Hence, it becomes necessary to model the nonlinear motion for realistic energy capture prediction. In this work, it is shown that a closed form energy optimal solution to the nonlinear model requires satisfaction of initial conditions that violate physical restrictions. Numerical optimization based controllers that use physical constraints as a necessary condition require large computation costs and are difficult to implement in real time. To mitigate computation costs for real-time implementation while precisely predicting nonlinear behavior, an efficient method of modelling WECs using an estimated linear model for computing the energy optimal control solution is presented. The estimated linear model is compared against the Cummins\u27 model for accuracy of motion during an uncontrolled case. It is also shown that, there exists a force which results in higher energy extraction than optimal force from Cummins\u27 model when applied to a nonlinear model. Additional analyses are also performed to evaluate the robustness of the proposed method in random and extreme sea states

A Simple and Effective Real-Time Controller for Wave Energy Converters

A novel strategy for the real-time control of oscillating wave energy converters (WECs) is proposed. The controller tunes the oscillation of the system such that it is always in phase with the wave excitation force and the amplitude of the oscillation is within given constraints. Based on a nonstationary, harmonic approximation of the wave excitation force, the controller is easily tuned in real-time for performance and constraints handling, through one single parameter of direct physical meaning. The effectiveness of the proposed solution is assessed for a heaving system in one degree of freedom, in a variety of irregular (simulated and real) wave conditions. A performance close to reactive control and to model predictive control is achieved. Additional benefits in terms of simplicity and robustness are obtained

EVALUATION OF VARIOUS WAVE ENERGY CONVERTERS IN THE BAY OF CÁDIZ

The Andalusian Agency of Energy has identified three areas of major interest for harnessing wave energy, in their plan of “Marine Energy and Energy Resources of Andalusia”. One of these areas is located on the Atlantic coast, the bay of Cádiz. Considering this initial interest, the objective of this work is to carry out an evaluation of the performance provided by various technologies of wave energy conversion in the bay of Cádiz. The data for the wave climate in the target area are obtained from the Spanish Agency Puertos del Estado. Diagrams for bivariate distributions of the sea states occurrences, defined by the significant wave height and the energy period, are shown. On this basis, the output of nine different technologies for the conversion of wave energy is assessed in the reference locations in the bay of Cádiz. According to the results obtained, it can be said that the bay of Cádiz is a suitable place for wave energy extraction

Robust control of wave energy converters

Energy-maximising controllers for wave energy devices are normally based on linear hydrodynamic device models. Such models ignore nonlinear effects which typically manifest themselves for large device motion (typical in this application) and may also include other modelling errors. In this paper, we present a methodology for reducing the sensitivity to modelling errors and nonlinear effects by the use of a hierarchical robust controller, which also allows good energy maximisation to be recovered through a passivity-based control approach

Desenvolvimento de protótipo para recuperação de energia das ondas

Currently, estimates indicate that electricity consumption will grow significantly in Europe and worldwide. This demand for electricity cannot be supported by fossil fuels, which led the European Union to set a goal of reducing traditional sources of non-renewable energy. The energy supply should tend to be supported by renewable sources. Wind and sun are among the most significant renewable energy sources. Ocean energy conversion technologies are still in the development, testing and experimental validation phase, with some of these devices having failed given the adversities of the environment in which they operate, which is the sea. These technologies incorporate, for the most part, complex mechanical systems, in which there is direct contact of the mechanisms with relative movements with the sea, and have resulted in reduced energy production and reduced operating life. This project presents the development of the electrical component of a device, whose concept has been developed, for a Power Take Off (PTO) mechanism, for the recovery of energy from sea waves.Atualmente, estimativas apontam que o consumo de eletricidade crescerá na Europa e a nível mundial de forma bastante significativa. Esta procura por energia elétrica não pode ser suportada por combustíveis fósseis, o que levou a União Europeia a estabelecer como objetivo a redução das fontes tradicionais de energia não-renovável. O fornecimento de energia deve ser tendencialmente suportado por fontes renováveis. O vento e o sol estão entre as fontes de energia renovável mais significativas. As tecnologias de conversão da energia dos oceanos ainda se encontram em fase de desenvolvimento, teste e validação experimental, tendo alguns desses dispositivos fracassado dadas as adversidades do meio onde operam, que é o mar. Estas tecnologias incorporam, na sua grande maioria, sistemas mecânicos complexos, em que tem contacto direto de mecanismos com movimentos relativos com o mar, e têm tido como resultado a reduzida produção de energia e o reduzido tempo de vida em operação. Neste projeto apresenta-se o desenvolvimento da componente elétrica de um dispositivo, cujo conceito tem vindo a ser desenvolvido, para um mecanismo Power Take Off (PTO) para a recuperação da energia das ondas do mar.Mestrado em Engenharia de Automação Industria

Robust control of wave energy converters

Energy-maximising controllers for wave energy devices are normally based on linear hydrodynamic device models. Such models ignore nonlinear effects which typically manifest themselves for large device motion (typical in this application) and may also include other modelling errors. In this paper, we present a methodology for reducing the sensitivity to modelling errors and nonlinear effects by the use of a hierarchical robust controller, which also allows good energy maximisation to be recovered through a passivity-based control approach

Soft Computing approaches in ocean wave height prediction for marine energy applications

El objetivo de esta tesis consiste en investigar el uso de técnicas de Soft Computing (SC) aplicadas a la energía producida por las olas o energía undimotriz. Ésta es, entre todas las energías marinas disponibles, la que exhibe el mayor potencial futuro porque, además de ser eficiente desde el punto de vista técnico, no causa problemas ambientales significativos. Su importancia práctica radica en dos hechos: 1) es aproximadamente 1000 veces más densa que la energía eólica, y 2) hay muchas regiones oceánicas con abundantes recursos de olas que están cerca de zonas pobladas que demandan energía eléctrica. La contrapartida negativa se encuentra en que las olas son más difíciles de caracterizar que las mareas debido a su naturaleza estocástica. Las técnicas SC exhiben resultados similares e incluso superiores a los de otros métodos estadísticos en las estimaciones a corto plazo (hasta 24 h), y tienen la ventaja adicional de requerir un esfuerzo computacional mucho menor que los métodos numérico-físicos. Esta es una de las razones por la que hemos decidido explorar el uso de técnicas de SC en la energía producida por el oleaje. La otra se encuentra en el hecho de que su intermitencia puede afectar a la forma en la que se integra la electricidad que genera con la red eléctrica. Estas dos son las razones que nos han impulsado a explorar la viabilidad de nuevos enfoques de SC en dos líneas de investigación novedosas. La primera de ellas es un nuevo enfoque que combina un algoritmo genético (GA: Genetic Algorithm) con una Extreme Learning Machine (ELM) aplicado a un problema de reconstrucción de la altura de ola significativa (en un boya donde los datos se han perdido, por ejemplo, por una tormenta) utilizando datos de otras boyas cercanas. Nuestro algoritmo GA-ELM es capaz de seleccionar un conjunto reducido de parámetros del oleaje que maximizan la reconstrucción de la altura de ola significativa en la boya cuyos datos se han perdido utilizando datos de boyas vecinas. El método y los resultados de esta investigación han sido publicados en: Alexandre, E., Cuadra, L., Nieto-Borge, J. C., Candil-García, G., Del Pino, M., & Salcedo-Sanz, S. (2015). A hybrid genetic algorithm—extreme learning machine approach for accurate significant wave height reconstruction. Ocean Modelling, 92, 115-123. La segunda contribución combina conceptos de SC, Smart Grids (SG) y redes complejas (CNs: Complex Networks). Está motivada por dos aspectos importantes, mutuamente interrelacionados: 1) la forma en la que los conversores WECs (wave energy converters) se interconectan eléctricamente para formar un parque, y 2) cómo conectar éste con la red eléctrica en la costa. Ambos están relacionados con el carácter aleatorio e intermitente de la energía eléctrica producida por las olas. Para poder integrarla mejor sin afectar a la estabilidad de la red se debería recurrir al concepto Smart Wave Farm (SWF). Al igual que una SG, una SWF utiliza sensores y algoritmos para predecir el olaje y controlar la producción y/o almacenamiento de la electricidad producida y cómo se inyecta ésta en la red. En nuestro enfoque, una SWF y su conexión con la red eléctrica se puede ver como una SG que, a su vez, se puede modelar como una red compleja. Con este planteamiento, que se puede generalizar a cualquier red formada por generadores renovables y nodos que consumen y/o almacenan energía, hemos propuesto un algoritmo evolutivo que optimiza la robustez de dicha SG modelada como una red compleja ante fallos aleatorios o condiciones anormales de funcionamiento. El modelo y los resultados han sido publicados en: Cuadra, L., Pino, M. D., Nieto-Borge, J. C., & Salcedo-Sanz, S. (2017). Optimizing the Structure of Distribution Smart Grids with Renewable Generation against Abnormal Conditions: A Complex Networks Approach with Evolutionary Algorithms. Energies, 10(8), 1097

[Report of] Specialist Committee V.4: ocean, wind and wave energy utilization

The committee's mandate was :Concern for structural design of ocean energy utilization devices, such as offshore wind turbines, support structures and fixed or floating wave and tidal energy converters. Attention shall be given to the interaction between the load and the structural response and shall include due consideration of the stochastic nature of the waves, current and wind

State-of-the-art of the most commonly adopted wave energy conversion systems

Copyright © 2023 The Authors. The vast diversity of wave energy conversion systems (WECSs) in the literature makes selecting the suitable WECS for wave energy harvest a stubborn process. This work summarizes six of the most widely adopted WECSs used heavily in previous research assessments and practical projects. This includes the Archimedes Wave Swing (AWS), the Wave Dragon (WD), Pelamis Wave Power (PWP), Aquabouy (AB), the Oyster, and the Oscillating Water Column (OWC). The work includes the mathematical modeling of these WECSs and the different projects and prototypes that involve these WECSs. Moreover, the latest research development in each of these WECSs is presented. Also, the wave energy potential in the world is discussed. Besides, the wave energy potential in Egypt, including that of the Mediterranean and the Red Sea, is discussed in detail. Furthermore, the steps required to perform a future feasibility study in Egypt and suggestions for the enhancement of an older study are provided. Finally, some suggestions and required equations are presented to explore the site power density and the most suitable WECS to be utilized in Egypt

Real-time Forecasting and Control for Oscillating Wave Energy Devices

Ocean wave energy represents a signicant resource of renewable energy and can make an important contribution to the development of a more sustainable solution in support of the contemporary society, which is becoming more and more energy intensive. A perspective is given on the benefits that wave energy can introduce, in terms of variability of the power supply, when combined with oshore wind. Despite its potential, however, the technology for the generation of electricity from ocean waves is not mature yet. In order to raise the economic performance of Wave energy converters (WECs), still far from being competitive, a large scope exists for the improvement of their capacity factor through more intelligent control systems. Most control solutions proposed in the literature, for the enhancement of the power absorption of WECs, are not implemented in practise because they require future knowledge of the wave elevation or wave excitation force. The non-causality of the unconstrained optimal conditions, termed complex-conjugate control, for the maximum wave energy absorption of WECs consisting of oscillating systems, is analysed. A link between fundamental properties of the radiation of the floating body and the prediction horizon required for an effective implementation of complex-conjugate control is identified. An extensive investigation of the problem of wave elevation and wave excitation force forecasting is then presented. The prediction is treated as a purely stochastic problem, where future values of the wave elevation or wave excitation force are estimated from past measurements at the device location only. The correlation of ocean waves, in fact, allows the achievement of accurate predictions for 1 or 2 wave periods into the future, with linear Autoregressive (AR) models. A relationship between predictability of the excitation force and excitation properties of the floating body is also identified. Finally, a controller for an oscillating wave energy device is developed. Based on the assumption that the excitation force is a narrow-banded harmonic process, the controller is effectively tuned through a single parameter of immediate physical meaning, for performance and motion constraint handling. The non-causality is removed by the parametrisation, the only input of the controller being an on-line estimate of the frequency and amplitude of the excitation force. Simulations in (synthetic and real) irregular waves demonstrate that the solution allows the achievement of levels of power capture that are very close to non-causal complex-conjugate control, in the unconstrained case, and Model predictive control (MPC), in the constrained case. In addition, the hierarchical structure of the proposed controller allows the treatment of the issue of robustness to model uncertainties in quite a straightforward and effective way