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Optimization and Energy Maximizing Control Systems for Wave Energy Converters...
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Optimization and Energy Maximizing Control Systems for Wave Energy Converters II

A special issue of Journal of Marine Science and Engineering (ISSN 2077-1312). This special issue belongs to the section "Ocean Engineering".

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 17433

Special Issue Editors

Dr. Giuseppe Giorgi

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Guest Editor
Marine Offshore Renewable Energy Lab (MOREnergy Lab), Department of Mechanical and Aerospace Engineering, Politecnico di Torino, 10129 Turin, Italy
Interests: marine energy; nonlinear hydrodynamics; wave–body interaction; energy-maximizing control systems; mooring systems; computational fluid dynamics; nonlinear dynamics; numerical modelling; optimization algorithms; numerical computing
Special Issues, Collections and Topics in MDPI journals
Dr. Mauro Bonfanti

E-Mail Website
Guest Editor
Marine Offshore Renewable Energy Lab (MOREnergy Lab), Department of Mechanical and Aerospace Engineering, Politecnico di Torino, 10129 Turin, Italy
Interests: marine energy; energy-maximizing control; hydraulic and mechanical PTO; nonlinear 6-DOF dynamics; optimal design; numerical modeling; experimental modeling; sustainable mobility; electric boat

Special Issue Information

Dear Colleagues,

In recent years, the European Union has advanced toward the adoption of renewable energy sources, pointing research efforts to the industrialization of clean energy extraction systems. Wave energy is now an established research field, and the scientific community focuses on reducing the capital cost associated with the design and construction of wave energy converters (WECs) while maximizing their performance and durability in real working conditions. Research challenges on WECs contemplate the application of well-known control and optimization techniques to highly nonlinear and multiple degrees of freedom dynamic systems. Different forms of traditional control have been purposed, such as path following or trajectory tracking, but WEC control aims to solve a multi-objective optimization problem: maximizing the net extracted energy while maintaining the WEC structural integrity and its durability. Furthermore, the design of a WEC system should underline accurate numerical models (nonlinear and nonideal) and optimal controls in order to perform a global techno-economic optimization.

We would like to invite papers on the topic of “Optimization and Energy-Maximizing Control Systems for Wave Energy Converters II”. This includes but is not limited to optimal design and control-informed optimization algorithms applied to WEC systems and array, model-based and data-driven novel energy-maximizing control strategies for WECs, numerical results and experimental tests proving the achievements of specific control architectures, specific challenges of the WEC application case, including strong nonlinearities (nonideal and saturated power take-off, hard-stop mechanisms), extreme condition handling (large motions and forces), and accurate estimation and forecasting of WEC input and states.

Dr. Giuseppe Giorgi
Dr. Mauro Bonfanti
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Journal of Marine Science and Engineering is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • wave energy converter
  • optimal design
  • energy-maximizing control
  • power conversion systems
  • estimation
  • forecasting
  • nonlinear modeling

Related Special Issue

Published Papers (10 papers)

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Research

26 pages, 2020 KiB  
Article
Measuring the Robustness of Optimal Design Solutions for Wave Energy Converters via a Stochastic Approach
by Filippo Giorcelli, Sergej Antonello Sirigu, Giuseppe Giorgi, Nicolás Faedo, Mauro Bonfanti, Jacopo Ramello, Ermanno Giorcelli and Giuliana Mattiazzo
J. Mar. Sci. Eng. 2024, 12(3), 482; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse12030482 - 13 Mar 2024
Viewed by 815
Abstract
Among the challenges generated by the global climate crisis, a significant concern is the constant increase in energy demand. This leads to the need to ensure that any novel energy systems are not only renewable but also reliable in their performance. A viable [...] Read more.
Among the challenges generated by the global climate crisis, a significant concern is the constant increase in energy demand. This leads to the need to ensure that any novel energy systems are not only renewable but also reliable in their performance. A viable solution to increase the available renewable energy mix involves tapping into the potential available in ocean waves and harvesting it via so-called wave energy converters (WECs). In this context, a relevant engineering problem relates to finding WEC design solutions that are not only optimal in terms of energy extraction but also exhibit robust behavior in spite of the harsh marine environment. Indeed, the vast majority of design optimization studies available in the state-of-the-art consider only perfect knowledge of nominal (idealized) conditions, neglecting the impact of uncertainties. This study aims to investigate the information that different robustness metrics can provide to designers regarding optimal WEC design solutions under uncertainty. The applied methodology is based on stochastic uncertainty propagation via a Monte Carlo simulation, exploiting a meta-model to reduce the computational burden. The analysis is conducted over a dataset obtained with a genetic algorithm-based optimization process for nominal WEC design. The results reveal a significant deviation in terms of robustness between the nominal Pareto set and those generated by setting different thresholds for robustness metrics, as well as between devices belonging to the same nominal Pareto frontier. This study elucidates the intrinsic need for incorporating robust optimization processes in WEC design. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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19 pages, 10387 KiB  
Article
Comparison of Advanced Control Strategies Applied to a Multiple-Degrees-of-Freedom Wave Energy Converter: Nonlinear Model Predictive Controller versus Reinforcement Learning
by Ali S. Haider, Kush Bubbar and Alan McCall
J. Mar. Sci. Eng. 2023, 11(11), 2120; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse11112120 - 6 Nov 2023
Viewed by 984
Abstract
Achieving energy maximizing control of a Wave Energy Converter (WEC) not only needs a comprehensive dynamic model of the system—including nonlinear hydrodynamic effects and nonlinear characteristics of Power Take-Off (PTO)—but to treat the entire system using an integrated approach, i.e., as a cyber–physical [...] Read more.
Achieving energy maximizing control of a Wave Energy Converter (WEC) not only needs a comprehensive dynamic model of the system—including nonlinear hydrodynamic effects and nonlinear characteristics of Power Take-Off (PTO)—but to treat the entire system using an integrated approach, i.e., as a cyber–physical system considering the WEC dynamics, control strategy, and communication interface. The resulting energy-maximizing optimization formulation leads to a non-quadratic and nonstandard cost function. This article compares the (1) Nonlinear Model Predictive Controller (NMPC) and (2) Reinforcement Learning (RL) techniques as applied to a class of multiple-degrees-of-freedom nonlinear WEC–PTO systems subjected to linear as well as nonlinear hydrodynamic conditions in simulation, using the WEC-Sim™ toolbox. The results show that with an optimal choice of RL agent and hyperparameters, as well as suitable training conditions, the RL algorithm is more robust under more stringent operating requirements, for which the NMPC algorithm fails to converge. Further, RL agents are computationally efficient on real-time target machines with a significantly reduced Task Execution Time (TET). Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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18 pages, 1452 KiB  
Article
On the Effect of Wave Direction on Control and Performance of a Moored Pitching Wave Energy Conversion System
by Bruno Paduano, Nicolás Faedo and Giuliana Mattiazzo
J. Mar. Sci. Eng. 2023, 11(10), 2001; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse11102001 - 17 Oct 2023
Viewed by 856
Abstract
In 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 [...] Read more.
In 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 50%, even though a prevalent wave direction exists at the site. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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16 pages, 1298 KiB  
Article
Model Predictive Energy-Maximising Tracking Control for a Wavestar-Prototype Wave Energy Converter
by Doudou Li and Ron Patton
J. Mar. Sci. Eng. 2023, 11(7), 1289; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse11071289 - 25 Jun 2023
Cited by 2 | Viewed by 1172
Abstract
To date, one of the main challenges in the wave energy field is to achieve energy-maximizing control in order to reduce the levelized cost of energy (LCOE). This paper presents a model predictive velocity tracking control method based on a hierarchical structure for [...] Read more.
To date, one of the main challenges in the wave energy field is to achieve energy-maximizing control in order to reduce the levelized cost of energy (LCOE). This paper presents a model predictive velocity tracking control method based on a hierarchical structure for a Wavestar-like deivce in the WEC-SIM benchmark. The first part of the system structure aims to estimate the wave excitation moment (WEM) by using a Kalman filter. Then, an extended Kalman filter (EKF) is chosen to obtain the amplitude and angular frequency of the WEM in order to compute the reference velocity. Following this, a low-level model predictive control (MPC) method is designed to ensure the wave energy converter (WEC) tracks the optimal reference velocity for maximum energy extraction from irregular waves. Two Gaussian Process (GP) models are considered to predict the future wave excitation moment and future reference velocity, which are needed in MPC design. The proposed strategy can give a new vision for energy-maximizing tracking control based on MPC. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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15 pages, 2075 KiB  
Article
Comparison of Offline, Real-Time Models and Hardware-in-the-Loop Test Results of a Power Take-Off for Wave Energy Applications
by Luca Castellini, Federico Gallorini, Giacomo Alessandri, Erick Fernando Alves, Dan Montoya, Bhavana Mudigonda and Elisabetta Tedeschi
J. Mar. Sci. Eng. 2022, 10(11), 1744; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse10111744 - 14 Nov 2022
Cited by 3 | Viewed by 1686
Abstract
The power take-off (PTO) of a wave energy converter (WEC) converts mechanical power extracted from the waves into electrical power. Increasing PTO performance under several operational conditions is therefore essential to reduce the levelized cost of energy of a given wave energy concept [...] Read more.
The power take-off (PTO) of a wave energy converter (WEC) converts mechanical power extracted from the waves into electrical power. Increasing PTO performance under several operational conditions is therefore essential to reduce the levelized cost of energy of a given wave energy concept and to achieve higher levels of technology readiness. A key task in the WEC design will then be the holistic assessment of the PTO performance in combination with other subsystems. It is hence important that WEC designers are aware of the different modeling options. This paper addresses this need and presents two alternative wave-to-wire modeling approaches based on a 250 kW modular electromechanical PTO coupled to an oscillating wave surge converter (OWSC) device. The first is a detailed and accurate offline model. The second model is a simplified and faster version of the first, being adequate for rapid analyses and real-time (RT) simulation. The paper presents the benchmarking of the offline model against the RT model and the hardware-in-the-loop (HIL) tests of the PTO. The normalized root-mean-square error (NRMSE) is considered as a quantitative indicator for the measurement of real-time and HIL test results against the offline simulation. Results show that the dynamics of the offline model are well represented by the RT model with execution times up to 10 times faster. The offline model also depicts well the behavior observed in the HIL tests with the NRMSE values for the PTO position, velocity, and force above 0.90, which shows the HIL test results replicates with fidelity the dynamic behavior of the complete model. Meaningful differences are however present and highlighted in this paper. An understanding of the advantages and drawbacks of these three approaches is fundamental to properly design a WEC during its project cycle and validate PTO concepts with a certain level of simplification. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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15 pages, 4583 KiB  
Article
Design and Research of Slope-Pendulum Wave Energy Conversion Device
by Zhanhong Wan, Ze Li, Dahai Zhang and Honghao Zheng
J. Mar. Sci. Eng. 2022, 10(11), 1572; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse10111572 - 24 Oct 2022
Cited by 4 | Viewed by 1701
Abstract
Wave energy is a kind of clean energy that is rich in reserves and has not been exploited on a large scale. The slope-pendulum wave energy conversion (S-PWEC) device has been optimized in structure and its capture efficiency has been increased. Taking the [...] Read more.
Wave energy is a kind of clean energy that is rich in reserves and has not been exploited on a large scale. The slope-pendulum wave energy conversion (S-PWEC) device has been optimized in structure and its capture efficiency has been increased. Taking the selection of the Zhejiang sea area as the research background, this paper performs numerical simulation and array WEC experimental testing of S-PWEC under 66 major sea conditions. The experimental results show that S-PWEC adds a slope structure to the bottom, which can effectively improve the motion response ability and resistance to extreme sea conditions. In the regular wave and irregular wave tests, the electron power output efficiency can be increased by 13.24% and 10.06%, respectively; in the array WEC experiment, the diffraction effect and radiation effect will affect the work of the array WEC, and the optimal arrangement distance can be selected to maximize the power output of the WEC system. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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31 pages, 17609 KiB  
Article
Improving Computational Efficiency in WEC Design: Spectral-Domain Modelling in Techno-Economic Optimization
by Mauro Bonfanti and Giuseppe Giorgi
J. Mar. Sci. Eng. 2022, 10(10), 1468; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse10101468 - 10 Oct 2022
Cited by 10 | Viewed by 2782
Abstract
Wave energy converter (WEC) optimization often underlines incremental and iterative approaches that result in suboptimal solutions, since all the elements that concur with a techno-economical evaluation are optimized separately due to computation constraints. A design process should rely on precise WEC models to [...] Read more.
Wave energy converter (WEC) optimization often underlines incremental and iterative approaches that result in suboptimal solutions, since all the elements that concur with a techno-economical evaluation are optimized separately due to computation constraints. A design process should rely on precise WEC models to ensure high result accuracy while minimizing the computational demand. These conflicting objectives can be addressed with non-linear time-domain models, known to be numerically accurate, and frequency-domain models due to their high computational efficiency. This work pursues the development of an all-encompassing optimization tool for a gyroscopic-type WEC called ISWEC that applies a new modelling technique named spectral-domain technique as a substitution to the complex time-domain model previously employed. In particular, the spectral-domain technique provides accurate and fast performance predictions of the ISWEC system and offers the possibility to model a hydraulic power take-off, not representable in the frequency domain. The article illustrates techno-economic trends associated with an early-stage design of the ISWEC in high-energy sea-sites, where the low-speed and high-torque profiles call for the use of hydraulic transmissions as opposed to the old electro-mechanical transmissions. The design tool proposed could facilitate the development of WEC technologies via efficient and accurate power assessment and via the possibility of carrying out advanced techno-economic optimisation that goes beyond linear models. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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22 pages, 1864 KiB  
Article
Downsizing the Linear PM Generator in Wave Energy Conversion for Improved Economic Feasibility
by Jian Tan, Xuezhou Wang, Henk Polinder, Antonio Jarquin Laguna and Sape A. Miedema
J. Mar. Sci. Eng. 2022, 10(9), 1316; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse10091316 - 17 Sep 2022
Cited by 7 | Viewed by 1676
Abstract
A crucial part of wave energy converters (WECs) is the power take-off (PTO) mechanism, and PTO sizing has been shown to have a considerable impact on the levelized cost of energy (LCOE). However, as a dominating type of PTO system in WECs, previous [...] Read more.
A crucial part of wave energy converters (WECs) is the power take-off (PTO) mechanism, and PTO sizing has been shown to have a considerable impact on the levelized cost of energy (LCOE). However, as a dominating type of PTO system in WECs, previous research pertinent to PTO sizing did not take modeling and optimization of the linear permanent magnet (PM) generator into consideration. To fill this gap, this paper provides an insight into how PTO sizing affects the performance of linear permanent magnet (PM) generators, and further the techno-economic performance of WECs. To thoroughly reveal the power production of the WEC, both hydrodynamic modeling and generator modeling are incorporated. In addition, three different methods for sizing the linear generator are applied and compared. The effect of the selection of the sizing method on the techno-economic performance of the WEC is identified. Furthermore, to realistically reflect the relevance of PTO sizing, wave resources from three European sea sites are considered in the techno-economic analysis. The dependence of PTO sizing on wave resources is demonstrated. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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30 pages, 5550 KiB  
Article
An Improved Hydraulic Power Take-Off Unit Based on Dual Fluid Energy Storage for Reducing the Power Fluctuation Problem in the Wave Energy Conversion System
by Mohd Afifi Jusoh, Zulkifli Mohd Yusop, Aliashim Albani, Muhamad Zalani Daud and Mohd Zamri Ibrahim
J. Mar. Sci. Eng. 2022, 10(8), 1160; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse10081160 - 21 Aug 2022
Cited by 2 | Viewed by 1989
Abstract
The power take-off (PTO) stability is one of the most important concerns for wave energy converters (WECs). The PTO unit converts the mechanical energy produced by the wave absorber (WA) unit into useful electrical energy. Due to the drastic input energy variation of [...] Read more.
The power take-off (PTO) stability is one of the most important concerns for wave energy converters (WECs). The PTO unit converts the mechanical energy produced by the wave absorber (WA) unit into useful electrical energy. Due to the drastic input energy variation of real wave motions, the generated electrical power from the PTO unit significantly fluctuates and is potentially harmful to electrical and electronic appliances. This paper proposes an improved hydraulic PTO (HPTO) for the WECs. An improved HPTO unit comprises a dual high-pressure accumulator (HPA) module and fluid energy control (FEC) module, which significantly enhances the generated electrical power from the generator under irregular wave circumstances. A complete model of wave absorber device with conventional and improved HPTO units was built in MATLAB/Simulink using a Simscape fluids toolbox. The parameters of the FEC control strategy were optimized using a genetic algorithm. The improved HPTO unit model was simulated with five irregular wave inputs to evaluate its performance in irregular conditions. The effects of the HPA pressure constraints on the improved HPTO unit performance were also investigated. Overall, the simulation results indicate that the improved HPTO unit was able to generate a stable power up to 87.3% of WECs in an irregular sea state. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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29 pages, 16001 KiB  
Article
Maximum Power Control Algorithm for Power Take-Off System Based on Hydraulic System for Floating Wave Energy Converters
by Chan Roh
J. Mar. Sci. Eng. 2022, 10(5), 603; https://0-doi-org.brum.beds.ac.uk/10.3390/jmse10050603 - 29 Apr 2022
Cited by 4 | Viewed by 2154
Abstract
In this study, a hydraulic system generator power converter was modeled to verify the performance of a hydraulic-based power take-off (PTO) system. Moreover, the characteristics and output performance of the PTO system were analyzed with various load control algorithms applied for maximum power [...] Read more.
In this study, a hydraulic system generator power converter was modeled to verify the performance of a hydraulic-based power take-off (PTO) system. Moreover, the characteristics and output performance of the PTO system were analyzed with various load control algorithms applied for maximum power control. The simulation performance was verified through a comparison with actual sea test results. Unlike previous studies on hydraulic-based PTO system control for input power performance, the performance of a hydraulic-based PTO system was analyzed through electrical load control in this study. The electrical load control was analyzed by applying a speed control algorithm based on the perturb and observe algorithm and an optimal torque control algorithm. A load control algorithm suitable for maximum power control of the PTO system was proposed by analyzing the characteristics and power generation performance of the system according to the control variables of each algorithm. The proposed optimal torque control algorithm proved to be suitable for maximum power control of the considered PTO system. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters II)
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