Yerai Peña Sanchez

• Doctor of Philosophy
• PostDoc Position at Mondragon University

Wave excitation force (torque) estimators, vital in wave energy systems, generally combine the nominal representation of a wave energy converter (WEC) with an excitation force (perturbation) model. Thus, this model-based estimation approach, grounded in the internal model principle, often employs two perturbation models: (i) the harmonic oscillator...

For a reliable development of energy-maximising optimal control strategies in wave energy, wave excitation force estimators are fundamental components in the control loop, since the optimality of the solution depends on their precision. In the control deployment phase, it is necessary to test the precision of wave estimates to assess the eventual m...

One of the key steps towards economic feasibility of wave energy conversion technology concerns scaling up to farms of multiple devices, in the attempt to reduce installation costs by sharing infrastructure, and a consequent drop in levelised cost of energy. Moreover, whenever wave energy systems are deployed in proximity (in so-called arrays), the...

This paper presents a novel Control Co-Design (CCD) methodology aimed at economically optimising the layout of wave energy converter (WEC) arrays. CCD ensures the synergy of optimised WEC and array parameters with the final control strategy, resulting in a comprehensive and efficient design of the array. By integrating a spectral-based control stra...

Motivated by the lack of comprehensive experimental implementation and assessment of the potential benefit that can be achieved with energy-maximising optimal control solutions for arrays of wave energy converters (WECs), we present, in this paper, the development, design, experimental implementation, and performance appraisal, of optimal moment-ba...

Model invalidation is the process of testing assumptions of a dynamical model by comparing simulated responses with experimental data, considering any discrepancies as evidence that the model may be invalid. In this study, a model invalidation methodology is presented, to obtain robust control oriented models for wave energy converters (WECs). In p...

The environmental impact of emissions of fossil fuels and their rising prices, together with countries' commitment to mitigate the effect of the alarming and rapid climate changes, have been a crucial thrust to investigate new solutions to have an energy supply depending on renewable energies. In this scenario, offshore wind-wave hybrid platforms h...

It is already well-known that the vast energy available in ocean waves can provide a massive contribution towards effective decarbonisation. Nonetheless, due to the irregular reciprocating motion of ocean waves, convergence towards a single type of technology becomes rather difficult, and tailored research, aiming at ultimately providing reliable W...

Ocean waves store an enormous amount of energy that is still untapped. Several wave energy converter (WEC) prototypes have already been suggested by different developers, but none of these prototypes has demonstrated economical viability, meaning that none of them is ready to compete in the energy market against other energy sources. In order to im...

Wave energy systems are designed to maximise energy absorption from the oscillatory motion of waves, which can make a crucial contribution in a new carbon free generation matrix [1]. Thus, the global ocean energy market (including wave and tidal) is expected to grow by more than 700\% by 2028 [2]. However, the harsh conditions faced in the ocean, t...

Optimal control strategies are a key development step towards commercialization of wave energy converters (WECs). Most of these rely on optimization routines to find a suitable control action to maximize WEC power production. Nevertheless, most of these solutions make use of device dynamical models, with the free-surface elevation as the external (...

Motion of wave energy converters (WECs) is usually exaggerated as a consequence of the application of control strategies for energy absorption maximisation. With the aim of preserving the physical integrity of the devices, constraint handling mechanisms, as part of the underlying control strategies, are considered a key component. Recent developmen...

Climate changes are increasingly impacting human welfare and, together with population growth, are rising the energy demand. To mitigate their negative effects, the need to harvest energy from renewable sources, while reducing the dependency on fossil fuels, has become pressing. This has led to the pursuit of new concepts that can exploit natural r...

Link to database: https://data.mendeley.com/datasets/n34wcksmts

In recent years, a framework for control of wave energy converters (WECs), termed moment-based control, has been developed within the wave energy conversion literature, exhibiting a remarkable performance in terms of energy absorption, while retaining real-time computational capabilities. Nonetheless, to date, practical results regarding moment-bas...

A key component of wave energy converters (WECs), which determines the technical and economic performance of WECs, is the power take-off (PTO) system. This WEC subsystem converts the hydrodynamic excitation of the WEC into useful mechanical and, typically, electrical energy. It is well known that WEC control systems have the capability to significa...

This paper proposes an optimal control strategy for wave energy devices subject to physical and nonlinear reactive power constraints. Using a pseudospectral Legendre method, optimization is carried out with energy maximization as a target. Physical limitations are applied to the WEC position, velocity, and controller, while a reactive power constra...

Within the wave energy community, hydrodynamic coefficients obtained from boundary element methods (BEMs) are commonly used to predict the behaviour of wave energy converters (WECs) in response to incident waves. A number of commercially-available BEM solvers exist, with a number of open-source alternatives also available. While open-source solvers...

The dynamics of a floating structure can be expressed in terms of Cummins’ equation, which is an integro-differential equation of the convolution class. In particular, this convolution operator accounts for radiation forces acting on the structure. Considering that the mere existence of this operator is highly inconvenient due to its excessive comp...

Wave energy has attracted significant attention during the past decades worldwide, due to the significant amount of energy available in ocean waves. However, to date, wave energy systems have not reached commercial viability. As such, appropriate control system technology is considered a key driver to achieve commercialisation of wave energy conver...

Within the wave energy community, hydrody-namic coefficients obtained from boundary element methods (BEMs) are commonly used to predict the behaviour of wave energy converters (WECs) in response to incident waves. A number of commercially-available BEM solvers exist, with a number of open-source alternatives also available. While open-source solver...

Due to the inherent relevance of passive (physically representative) models for control, state-estimation, and motion simulation in the field of marine systems, in this paper, an optimisation-based approach to passivation of linear time-invariant (LTI) systems is proposed with application to physically consistent dynamical modelling of marine struct...

Boundary Element Method (BEM) solvers are extensively used to obtain the hydrodynamic coefficients required to model hydrodynamic forces in floating marine structures. BEM solvers require the discretization of the submerged device surface as a mesh to compute the hydro-dynamic coefficients as radiation damping and added mass, response amplitude ope...

Wave energy converters (WECs) need to be optimally controlled to be commercially viable. These controllers often require an estimate of the (unmeasurable) wave excitation force. To date, observers for WECs are often based upon ‘complex’ techniques, which are counter-intuitive in their design, additionally requiring an explicit model to describe the...

This study addresses the experimental validation of a linear time-invariant (LTI) energy-maximizing control strategy for wave energy converters (WECs), applied to a 1/20 scale Wavestar WEC. To fulfill this objective, system identification routines are utilized to compute a mathematical (parametric) model of the input-output dynamics of the device,...

The motion of a wave energy converter (WEC) can be described in terms of an integro-differential equation, which involves a convolution operator. This convolution term accounts for the effect of radiation forces acting on the device and represents a computational and representational drawback both for simulation and analysis/design of control/estim...

Numerical wave tanks (NWTs) provide efficient test beds for the numerical analysis at various stages during the development of wave energy converters (WECs). To ensure the acquisition of accurate, high-fidelity data sets, validation of NWTs is a crucial step. However, using experimental data as reference during model validation, exact knowledge of...

Considering the Wave Star wave energy converter (WEC), which is a standard point absorber prototype, this study addresses the complete energy maximising control design procedure. The WEC model is obtained using system identification routines. Then, using the identified model, a LTI energy maximising control strategy, recently presented in the liter...

In this study, we address the issue of real-time energy-maximising control for wave energy converters (WECs), by proposing a receding-horizon optimal control framework based on the concept of a moment. This approach is achieved by extending the so-called moment-based framework, recently published in the WEC literature, to effectively solve the asso...

Energy-maximising control of wave energy converters can be separated into two different classes: optimisation and non-optimisation based strategies. While optimisation-based controllers can outperform non-optimisation based strategies, the computational requirements associated with numerical optimisation routines, and the high control forces requir...

When it comes to parameterisation of dynamical models for arrays of Wave Energy Converters (WECs), the most-used approach, within the wave energy literature, provides a state-space representation whose order (dimension) increases quadratically with the number of devices composing the WEC array. This represents a major drawback for key WEC design el...

A Linear Time Invariant (LTI) energy-maximising control strategy for Wave Energy Converters (WECs) is proposed in this paper. Using the fundamental requirement of impedance-matching, the controller is tuned to maximise the energy obtained under polychromatic wave excitation. Given the LTI nature of the proposed controller, the design and implementa...

Considering the Wave Star wave energy converter (WEC), which is a standard point absorber prototype, this study addresses the complete energy maximising control design procedure. The WEC model is obtained using system identification routines. Then, using the identified model, a LTI energy maximising control strategy, recently presented in the liter...

The implementation of energy-maximizing control systems (EMCSs) can significantly increase the efficiency and economic viability of resonant wave-energy converters (WECs). To achieve optimal control and drive the WEC into resonance with the incoming wave field, knowledge of the wave excitation force is required. In operational conditions, this quan...

Cummins' equation is commonly used to describe the motion of Wave Energy Converters (WECs), where the radiation force is characterised by a convolution operation. The computational effort associated with the solution of the convo-lution term, often represents a drawback for e.g. optimisation or exhaustive-search studies. To overcome this disadvanta...

We present in this paper a moment-matching method to compute a parametric approximation of the input-output (force-to-motion) response of a multiple Degree of Freedom (DoF) Wave Energy Converter (WEC), based on the algorithm presented in [1]. This method allows the user to select a set of interpolation frequencies where the approximating model exac...

The motion of a Wave Energy Converter (WEC) can be described in terms of an integro-differential equation, which involves a con-volution operator. This convolution term accounts for the effect of radiation forces acting on the device, and represents a computational and representational drawback both for simulation, and analysis/design of control/es...

Within the ocean engineering literature, and, particularly, within the wave energy research and hydrodynamic fields, different methods can be found that aim to identify a finite-order para-metric model to represent the radiation force convolution term of the well-known Cummins' equation. Such an approximation process is required for several reasons...

Cummins' equation is commonly used to describe the motion of Wave Energy Converters (WECs), where the radiation force is characterised by a convolution operation. The computational effort associated with the solution of the convolution term often represents a drawback for e.g. optimisation or exhaustive-search studies. To overcome this disadvantage...

For wave energy converter control applications, autoregressive (AR) models have been proposed as a simple wave forecasting method, solely based on measured or estimated values of the past wave elevation (or excitation force) signal. Using offline-filtered wave time series, AR models can achieve accurate forecasts several wave periods into the futur...

The motion of a Wave Energy Converter (WEC) can be described in terms of a particular integro-differential equation, which involves a convolution product accounting for the radiation forces. This convolution term has a computational and a representational drawback both for simulation, and for analysis/design of control strategies. This study presen...

The motion of a Wave Energy Converter (WEC) can be described in terms of an integro-differential equation, which involves a convolution product. The convolution term, which accounts for the radiation forces, represents a computational and representational drawback both for simulation, and analysis/design of control strategies. Several studies attem...

Several methods have been developed to identify a parametric model that represents the radiation force convolution term in Cummins’ equation. The reason behind such an approximation is twofold: obtaining a model with less computational (effort) requirements, and easing model-based control design procedures. In this paper, a case study on the param...

To maximise energy conversion, real-time control of a Wave Energy Converter (WEC) requires knowledge of the present and future excitation force (F $_{\rm ex}$ ) acting on the device, which is a non-measurable quantity. The problem of estimation and forecasting of F $_{\rm ex}$ becomes more challenging when arrays of WECs are considered, due to the...

In order to extract as much energy as possible from ocean waves, an optimal control must be implemented in a wave energy converter (WEC), which requires the knowledge of the future incident waves (η). One of the most used methods to predict the future η, is to use a linear combination of past η values. Several models can be found in the literature,...