Optimum Reactive Control and Control by Latching of a Wave-Absorbing Semisubmerged Heaving Sphere

2002 ◽  
Author(s):  
Jo̸rgen Hals ◽  
Torkel Bjarte-Larsson ◽  
Johannes Falnes
Keyword(s):  
Phase Control ◽  
Energy Output ◽  
Reactive Control ◽  
Wave Energy Converters ◽  
Submerged Sphere ◽  
Sphere Radius ◽  
Absorbed Power ◽  
S Period ◽  
And Control ◽  
Incident Waves

The theoretical potential for maximising energy output of wave-energy converters by means of optimum control is quantified for a heaving semi-submerged sphere on deep water. The heave amplitude is constrained to not exceed 0.6 units of the radius. Sinusoidal incident waves of amplitudes up to 3 m and period in the range of 6 s to 12 s are considered, when the sphere radius is 5 m. Optimum reactive control, contrary to sub-optimal latching phase control, requires ability for reversing the energy flow through the power take-off machinery. Computed results show that, for a typical wave of 0.5 m amplitude and 9 s period, the maximum absorbed power is 24, 137, and 172 kW for the cases of no phase control (passive system), sub-optimal latching control, and ideally optimal reactive control, respectively. The ratio between the maximum/minimum instantaneous power and the average absorbed power is 2/0, 4.1/0 and 11.0/-9.0, respectively, for the three different strategies.

Ocean Wave Energy Converters and Control Methodologies

2013 ◽  
Author(s):  
Jingjin Xie ◽  
Lei Zuo
Keyword(s):  
Wave Energy ◽  
Ocean Wave ◽  
Reactive Control ◽  
Floating Bodies ◽  
Point Absorber ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Latching Control ◽  
And Control ◽  
Energy Converters

Ocean wave energy is an indirect form of solar energy with great potential worldwide. Technologies on extracting energy from the ocean wave have been explored for centuries and are still undergoing with challenges. The nature of ocean wave and ocean wave energy are introduced with their mathematical models in this paper. The features and working principles of three forms of mainstream ocean wave energy converters (OWEC), including floating bodies (point absorber, attenuator, and terminator), oscillating water column (OWC) and wave overtopping, are presented together with their hydrodynamic performances. The corresponding control methodologies for these ocean wave energy converters, such as latching control, declutch control, reactive control, model predictive control (MPC), etc., are analyzed in a comprehensive manner thereafter. Optimal conditions for maximum power absorption are also introduced with mathematical modeling and derivations.

scholarly journals Hardware-in-the-Loop Validation of Model Predictive Control of a Discrete Fluid Power Power Take-Off System for Wave Energy Converters

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3668
Author(s):  
Anders H. Hansen ◽  
Magnus F. Asmussen ◽  
Michael M. Bech
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Wave Energy ◽  
Fluid Power ◽  
Wave Power ◽  
Reactive Control ◽  
Power Extraction ◽  
Wave Energy Converters ◽  
Extraction Algorithm ◽  
Energy Converters

Model predictive control based wave power extraction algorithms have been developed and found promising for wave energy converters. Although mostly proven by simulation studies, model predictive control based algorithms have shown to outperform classical wave power extraction algorithms such as linear damping and reactive control. Prediction models and objective functions have, however, often been simplified a lot by for example, excluding power take-off system losses. Furthermore, discrete fluid power forces systems has never been validated experimentally in published research. In this paper a model predictive control based wave power extraction algorithm is designed for a discrete fluid power power take-off system. The loss models included in the objective function are based on physical models of the losses associated with discrete force shifts and throttling. The developed wave power extraction algorithm directly includes the quantized force output and the losses models of the discrete fluid power system. The experimental validation of the wave power extraction algorithm developed in the paper shown an increase of 14.6% in yearly harvested energy when compared to a reactive control algorithm.

scholarly journals Control-Influenced Layout Optimization of Arrays of Wave Energy Converters

2014 ◽  
Author(s):  
Philip Balitsky ◽  
Giorgio Bacelli ◽  
John V. Ringwood
Keyword(s):  
Wave Climate ◽  
Radiative Properties ◽  
Optimal Layout ◽  
Wave Direction ◽  
Sea State ◽  
Wave Energy Converters ◽  
Control Schemes ◽  
And Control ◽  
Tuning Scheme ◽  
Optimal Configurations

In this paper we compare the optimal configurations for an array of WECs given two control schemes, a real-time global control and a passive sea-state based tuning scheme. In a particular wave climate and array orientation with its axis normal to the prevailing wave direction, closely-spaced symmetrical arrays of 2, 3, 4, 5, and 6 cylinders of different radiative properties are simulated for varying inter-device separation distances. For each device and control type, we focus on the factors that influence the optimal layout, including number of devices, separating distance and angular spreading. The average annual power output is calculated for each optimal configuration.

Performance assessments of the fully submerged sphere and cylinder point absorber wave energy converters

2019 ◽  
Vol 33 (13) ◽  
pp. 1950168 ◽  
Author(s):  
Qianlong Xu ◽  
Ye Li ◽  
Yingkai Xia ◽  
Weixing Chen ◽  
Feng Gao
Keyword(s):  
Wave Height ◽  
Wave Energy ◽  
Interaction Analysis ◽  
Wave Power ◽  
Viscous Damping ◽  
Power Performance ◽  
Point Absorber ◽  
Wave Energy Converters ◽  
Submerged Sphere ◽  
Energy Converters

Fully submerged sphere and cylinder point absorber (PA), wave energy converters (WECs) are analyzed numerically based on linearized potential flow theory. A boundary element method (BEM) (a radiation–diffraction panel program for wave-body interactions) is used for the basic wave-structure interaction analysis. In the present numerical model, the viscous damping is modeled by an equivalent linearized damping which extracts the same amount of wave energy over one cycle as the conventional quadratic damping term. The wave power capture width in each case is predicted. Comparisons are also made between the sphere and cylinder PAs which have identical geometrical scales and submerged depths. The results show that: (i) viscous damping has a greater influence on wave power performance of the cylinder PA than that of the sphere PA; (ii) the increasing wave height reduces wave power performance of PAs; (iii) the cylinder PA has a better wave power performance compared to the sphere PA in larger wave height scenarios, which indicates that fully submerged cylinder PA is a preferable prototype of WEC.

Emulation and Control Methods for Direct Drive Linear Wave Energy Converters

2013 ◽  
Vol 9 (2) ◽  
pp. 790-798 ◽  
Author(s):  
Zanxiang Nie ◽  
Xi Xiao ◽  
Richard McMahon ◽  
Peter Clifton ◽  
Yunxiang Wu ◽  
...  
Keyword(s):  
Wave Energy ◽  
Linear Wave ◽  
Control Methods ◽  
Direct Drive ◽  
Wave Energy Converters ◽  
And Control ◽  
Energy Converters

scholarly journals Wave Energy Assessment at Valencia Gulf and Comparison of Energy Production of Most Suitable Wave Energy Converters

2020 ◽  
Vol 17 (22) ◽  
pp. 8473
Author(s):  
Raúl Cascajo ◽  
Emilio García ◽  
Eduardo Quiles ◽  
Francisco Morant ◽  
Antonio Correcher
Keyword(s):  
Renewable Energy ◽  
Wave Energy ◽  
Energy Demand ◽  
Alternative Energy ◽  
Average Energy ◽  
Wave Climate ◽  
Energy Output ◽  
Renewable Sources ◽  
Wave Energy Converters ◽  
Energy Converters

Seaports’ energy strategy should rely on the use of renewable energy. Presently, the share of renewable energy used by many of the ports worldwide is negligible. Some initiatives are in the process of implementation to produce some of the energy used by the Port of Valencia, one the largest ports in the Mediterranean Basin. Among these initiatives, a photovoltaic plant with an installed capacity of 5.5 MW is under a tendering process and the assessment studies for the deployment of three to five windmills are close to being finished. However, this is not enough to make it a “zero emissions port” as some of the energy demand would still be covered by fossil fuels. Therefore, we should consider clean alternative energy sources. This article analyses the wave energy resources in the surroundings of the Port of Valencia using a 7-year series of data obtained from numerical modelling (forecast). The spatial distribution of wave power is analysed using data from 3 SIMAR points at Valencia Bay and is compared to the data obtained by the Valencia Buoy I (removed in 2005). The obtained results are used to estimate the power matrices and the average energy output of two wave energy converters suitable to be integrated into the port’s infrastructure. Finally, the wave energy converters’ production is compared to the average amount of energy that is forecast to be obtained from other renewable sources such as solar and wind. Due to the nature of the Gulf’s wave climate (mostly low waves), the main conclusion is that the energy obtainable from the waves in the Valencia Gulf will be in correlation with such climate. However, when dealing with great energy consumers every source of production is worthwhile and further research is needed to optimize the production of energy from renewable sources and its use in an industrial environment such as ports.

A Comparison of Selected Strategies for Adaptive Control of Wave Energy Converters

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Jørgen Hals ◽  
Johannes Falnes ◽  
Torgeir Moan
Keyword(s):  
Wave Energy ◽  
Reactive Power ◽  
Average Power ◽  
Volume Ratio ◽  
External Input ◽  
Irregular Waves ◽  
Optimal Velocity ◽  
Wave Energy Converters ◽  
Absorbed Power ◽  
Energy Converters

Wave-energy converters of the point-absorbing type (i.e., having small extension compared with the wavelength) are promising for achieving cost reductions and design improvements because of a high power-to-volume ratio and better possibilities for mass production of components and devices as compared with larger converter units. However, their frequency response tends to be narrow banded, which means that the performance in real seas (irregular waves) will be poor unless their motion is actively controlled. Only then the invested equipment can be fully exploited, bringing down the overall energy cost. In this work various control methods for point-absorbing devices are reviewed, and a representative selection of methods is investigated by numerical simulation in irregular waves, based on an idealized example of a heaving semisubmerged sphere. Methods include velocity-proportional control, approximate complex conjugated control, approximate optimal velocity tracking, phase control by latching and clutching, and model-predictive control, all assuming a wave pressure measurement as the only external input to the controller. The methods are applied for a single-degree-of-freedom heaving buoy. Suggestions are given on how to implement the controllers, including how to tune control parameters and handle amplitude constraints. Based on simulation results, comparisons are made on absorbed power, reactive power flow, peak-to-average power ratios, and implementation complexity. Identified strengths and weaknesses of each method are highlighted and explored. It is found that overall improvements in average absorbed power of about 100–330% are achieved for the investigated controllers as compared with a control strategy with velocity-proportional machinery force. One interesting finding is the low peak-to-average ratios resulting from clutching control for wave periods about 1.5 times the resonance period and above.

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