Model predictive control of sea wave energy converters – Part II: The case of an array of devices

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Guang Li and Mike R. Belmont, Renewable Energy – August 2014

Abstract

This paper addresses model predictive control (MPC) of highly-coupled clusters of sea wave energy converters (WECs). Since each WEC is not only a wave absorber but also a wave generator, the motion of each WEC can be affected by the waves generated by its adjacent WECs when they are close to each other. A distributed MPC strategy is developed to maximize the energy output of the whole array and guarantee the safe operation of all the WECs with a reasonable computational load. The system for an array is partitioned into subsystems and each subsystem is controlled by a local MPC controller. The local MPC controllers run cooperatively by transmitting information to each other. Within one sampling period, each MPC controller performs optimizations iteratively so that a global optimization for the whole array can be approximated. The computational burden for the whole array is also distributed to the local controllers. A numerical simulation demonstrates the efficacy of the proposed control strategy. For the WECs operating under constraints explored, it is found that the optimized power output is an increasing function of degree of WEC–WEC coupling. Increases in power of up to 20% were achieved using realistic ranges of parameters with respect to the uncoupled case.

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Model predictive control of sea wave energy converters – Part I: A convex approach for the case of a single device

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Guang Li and Michael R Belmont, Renewable Energy – September 2014

Abstract

This paper investigates model predictive control (MPC) of a single sea wave energy converter (WEC). By using control schemes which constrain certain quantities, such as the maximum size of the feedback force, the energy storage for actuators and relative heave motion, it is possible for control to not only improve performance but to directly impact strongly on design and cost. Motivated by this fact, a novel objective function is adopted in the MPC design, which brings obvious benefits: First, the quadratic program (QP) derived from this objective function can be easily convexified, which facilitates the employment of existing efficient optimization algorithms. Second, this novel design can trade off the energy extraction, the energy consumed by the actuator and safe operation. Moreover, an alternative QP is also formulated with the input slew rate as optimization variable, so that the slew rate limit of an actuator can be explicitly incorporated into optimization. All these benefits promote the real-time application of MPC on a WEC and reduced cost of hardware.

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Multistable chain for ocean wave vibration energy harvesting

R. L. Harne, M. E. Schoemaker, and K. W. Wang – Proc. SPIE Active and Passive Smart Structures and Integrated Systems, March 2014

Abstract

The heaving of ocean waves is a largely untapped, renewable kinetic energy resource. Conversion of this energy into electrical power could integrate with solar technologies to provide for round-the-clock, portable, and mobile energy supplies usable in a wide variety of marine environments. However, the direct drive conversion methodology of grid integrated wave energy converters does not efficiently scale down to smaller, portable architectures. This research develops an alternative power conversion approach to harness the extraordinarily large heaving displacements and long oscillation periods as an excitation source for an extendible vibration energy harvesting chain. Building upon related research findings and engineering insights, the proposed system joins together a series of dynamic cells through bistable interfaces.

Energy Extraction from Shallow Tidal Flows

Jack William Giles – University of Southampton, PhD Dissertation, December 2013

Abstract

Over the past decade within the renewable energy sector a strong research and development focus has resulted in the growth of an embryonic tidal stream energy industry. Previous assessments of the tidal stream resource appear to have neglected shallow tidal flows. This resource located in water depths of 10-30m is significant because it is generally more accessible for energy extraction than deeper offshore tidal sites and hence a good location for first generation tidal stream arrays or fences. The close proximity to shore may lead to improvements in construction feasibility and economic prospects. The objective of this project is to investigate several aspects concerning the exploitation of shallow tidal flows for energy extraction. Fundamental to this project is the importance of developing research alongside and in conjunction with industrial shallow water
prototype projects.

Evaluation of technologies for harvesting wave energy in Caspian Sea

Rezvan Alamian, Rouzbeh Shafaghat, S. Jalal Miri, Nima Yazdanshenas, and Mostafa Shakeri – Renewable and Sustainable Energy Reviews, April 2014

Abstract

Ocean is one of the renewable sources of energy that can supply part of the world’s energy needs and thus reduce the rate of consumption of fossil fuels and other non-renewable resources. The wave energy can be converted to electricity or other forms of usable energy. Water waves have a relatively high power density with a total global power of approximately 1–10 TW, equivalent to a large fraction of the world’s current total energy consumption. This study is aimed at evaluating the existing systems for converting the wave energy into electricity with the idea in mind that they could be used in the Caspian Sea, with average wave energy of 5–14 kW/m.

Two-Dimensional Geometric Optimization of an Oscillating Water Column Converter of Real Scale

Mateus das Neves Gomes, Elizaldo Domingues dos Santos, Liércio André Isoldi, and Luiz Alberto Oliveira Rocha – 22nd International Congress of Mechanical Engineering, November 2013

Abstract

The present paper presents a two-dimensional numerical study about the geometric optimization of an ocean Wave Energy Converter (WEC) into electrical energy. The operational principle is based on the Oscillating Water Column (OWC). The main goal is to seek for the optimal geometry which maximizes the absorbed power take off (PTO) when it is subjected to a defined wave climate. To do so, Constructal Design is employed varying the degree of freedom (DOF) H₁/L (ratio between the height and length of OWC chamber) and H₃ (lip submergence), while the other DOF H₂/l (ratio between height and length of chimney) is kept fixed.

Obtaining renewable energy from tidal currents in the Aviles port: New services for citizens

Alvarez, E.Alvarez; Manso, A.Navarro; Gutierrez-Trashorras, A.J.; Francos, Joaquin Fernandez; Secades, M.Rico – 2013 International Conference on New Concepts in Smart Cities: Fostering Public and Private Alliances (SmartMILE), December 2013

Abstract

The port of Avilés is very tightly integrated in the city of Avilés. Within the waters of the port there is significant tidal activity. The possibility of extracting this tidal energy and using it locally to provide services for citizens and port activities is a topic of great interest. Despite the low viability of current tidal energy installations, this investigation includes a design for a micro-generator system based on a set of micro-turbines and the associated off-the-shelf electronic converters to be situated in the port of Avilés. A study of the energy production system and its economic feasibility provide the parameters to define suitable sites for the installation.

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Adaptive damping power take-off control for a three-body wave energy converter

Zhe Zhang, Brekken, T., Rhinefrank, K., Schacher, A., Prudell, J., Hammagren, E., and Lenee-Bluhm, P. – 2013 IEEE Energy Conversion Conference and Exposition (ECCE), September 2013

Abstract

The performance of the power take-off (PTO) system for a wave energy converter (WEC) depends largely on its control algorithm. This paper presents an adaptive damping control algorithm which improves power capture across a range of sea states. The comparison between this control algorithm and other active control approaches such as linear damping is presented. Short term wave elevation forecasting methods and wave period determination methods are also discussed as pre-requirements for this method. This research is conducted for a novel WEC, developed by Columbia Power Technologies. All hydrodynamic models are validated with their 1:7 and 1:33 scale tests.

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Efficiency of OWC wave energy converters: A virtual laboratory

I. López and G. Iglesias – Applied Ocean Research, January 2014

Abstract

The performance of an oscillating water column (OWC) wave energy converter depends on many factors, such as the wave conditions, the tidal level and the coupling between the chamber and the air turbine. So far most studies have focused on either the chamber or the turbine, and in some cases the influence of the tidal level has not been dealt with properly. In this work a novel approach is presented that takes into account all these factors.

Wave-power absorption from a finite array of oscillating wave surge converters

E. Renzi, A. Abdolali, G. Bellotti, and F. Dias – Renewable Energy, March 2014

Abstract

Semi-analytical and fully numerical modelling is developed in the framework of the inviscid potential flow theory to investigate the dynamics of a wave farm made by flap-type wave energy converters in the nearshore. The hydrodynamic parameters and the efficiency of the system in typical layouts are calculated with both models. Good agreement is shown between the two approaches. Parametric analysis undertaken with the semi-analytical model allows to identify a near-resonant phenomenon which is responsible for increasing the absorbed power by the single elements of the array. Such result could be used as a preliminary design criterion. The numerical model is then applied to analyse a configuration of practical engineering interest, i.e. an array of two staggered converters. The dynamics arising in this more complex system is explained, showing that non-symmetric layouts can be less effective.

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