Tag Archives: System Development

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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Filed under Modeling, System Development, Wave

Experimental wave termination in a 2D wave tunnel using a cycloidal wave energy converter


SG Siegel, C Fagley, S Nowlin – Applied Ocean Research, October 2012

Abstract

A lift based cycloidal wave energy converter (CycWEC) is investigated in a 1:300 scale two-dimensional wave flume experiment. This type of wave energy converter consists of a shaft with one or more hydrofoils attached eccentrically at a radius. The main shaft is aligned parallel to the wave crests and submerged at a fixed depth. The operation of the CycWEC both as a wave generator as well as a wave-to-shaft energy converter interacting with straight crested waves is demonstrated. The geometry of the converter is shown to be suitable for wave termination of straight crested harmonic and irregular waves. The impact of design parameters such as device size, submergence depth, and number of hydrofoils on the performance of the converter is shown. For optimal parameter choices, experimental results demonstrate energy extraction efficiencies of more than 95% of the incoming wave energy. This is achieved using feedback control to synchronize the rotation of the CycWEC to the incoming wave, and adjusting the blade pitch angle in proportion to the wave height. Due to the ability of the CycWEC to generate a single sided wave with few harmonic waves, little energy is lost to waves radiating in the up-wave and down-wave directions.

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THOR’s Power Method for Hydrokinetic Devices


J.T. Hunt and J. Rumker – Technical Report submitted to DOE EERE Wind & Water Power Program, August, 2012

Abstract
Ocean current energy represents a vast untapped source of renewable energy that exists on the outer continental shelf areas of the 5 major continents. Ocean currents are unidirectional in nature and are perpetuated by thermal and salintiy sea gradients, as well as coriolis forces imparted from the earth’s rotation. This report details THORs Power Method, a breakthrough power control method that can provide dramatic increases to the capacity factor over and above existing marine hydrokinetic (MHK) devices employed in the extraction of energy from ocean currents. THORs Power Method represents a constant speed, variable depth operational method that continually locates the ocean current turbine at a depth at which the rated power of the generator is routinely achieved. Variable depth operation is achieved by using various vertical force effectors, including ballast tanks for variable weight, a hydrodynamic wing for variable lift or down force and drag flaps for variable vehicle drag forces.

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Dynamics and optimization of the OWC spar buoy wave energy converter


AFO Falcão, JCC Henriques, JJ Cândido – Renewable Energy, December 2012

Abstract
The paper concerns the hydrodynamic analysis and optimization of an OWC spar buoy, possibly the simplest concept for a floating oscillating water column (OWC) wave energy converter. It is an axisymmetric device consisting basically of a submerged vertical tail-tube-fixed to an axisymmetric floater that oscillates essentially in heave. The air flow displaced by the water motion inside the tube drives a self-rectifying air turbine. The possible advantages of using a tube of non-uniform inner cross section are investigated theoretically and numerically, especially as a way of reducing the draught of the device without significantly impairing its power performance. The unsteady water flow in the tube is modelled as one-dimensional. The frequency-dependent hydrodynamic coefficients of the tube-floater pair were computed with a boundary-element code. A linear air turbine is assumed. The hydrodynamics of the wave energy absorption is analysed in the frequency domain, including the effect of air compressibility in the chamber; special attention is devoted to optimization. Numerical results are presented for device’s performance in regular and irregular waves, including especially optimization of the tube geometry and of the turbine characteristic. Practical implications of these results are discussed.

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Filed under Modeling, System Development

Neural control for voltage dips ride-through of oscillating water column-based wave energy converter equipped with doubly-fed induction generator


M Alberdi, M Amundarain, A Garrido, I Garrido – Renewable Energy, December 2012

Highlights
The most demanded skill during voltage drops is a fault-ride-through capability. ► The innovative aspect exploited in this paper is the application of a neural control. ► The controller changes the references according to the pressure drop and voltage dip. ► The neural controller achieves the uninterrupted operation of the wave energy plant.

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Filed under Modeling, System Development

Multi-arrayed tidal current energy farm and the integration method of the power transportation


CH Jo, KH Lee, JH Lee, C Nichita – 2012 International Symposium on Power Electronics, Electrical Drives, Automation, and Motion, June  2012

Abstract
Ocean energy resources are attractive renewable supply options for Korea being surround by ocean. Also having very strong tidal current speeds, there are many suitable sites for the application of TCP (Tidal Current Power) on the west and south coastal region in Korea with the maximum current speed of up to 6.5m/s. Not like other renewable energy sources, TCP is the high reliable and predictable and continuous energy source as the current pattern and speed can be predicted throughout the year. Since the large scale tidal current farm consists of many units of the turbine devices, the interaction effect is very important in power production. Also the power integration method in ocean energy has of very important issue. In this paper, the interaction effect and the power connection methods for each turbine unit and the integration method for 200MW tidal current farm are conceptually introduced with the offshore power integration platform

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Filed under Component Development, System Development

An overview of hydraulic systems in wave energy application in China


D Zhang, W Li, Y Lin, J Bao – Renewable and Sustainable Energy Reviews, September 2012

Abstract
Wave energy is being increasingly regarded in China as a major and promising resource. There are many different ways to convert wave energy to electricity and some other energy. Hydraulic systems are used most widely in some of them to realize this conversion. An overview of hydraulic systems in wave energy application as well as the relevant technologies in China is given in this article. Some basic principles are presented, assessment and advices are shown for each category. Some suggestions of the outlook of hydraulic systems in wave energy application are also given.

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Synchronized control of cross-flow-water-turbine-based twin towers


M Vallet, I Munteanu, AI Bratcu, S Bacha, D Roye – Renewable Energy, June 2012

Highlights
► A system composed of cross-flow-water-turbine-based twin vertical towers is studied. ► The angular position synchronization of the two towers is ensured by control action. ► This approach is similar to the phase-locked loop techniques used in electronics. ► Real-time experiments on a power hardware-in-the-loop simulator have been carried out. ► The results sustain the reliability and effectiveness of the approach.

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Filed under Instrumentation, System Development

Narec aiming high


D Hopwood – Renewable Energy Focus, May 2012

Summary
Steelwork is being erected on the site of a new £45m turbine drive train testing facility at the National Renewable Energy Centre (Narec) in Northumberland, UK. When complete it could be the most advanced of its type in the world.

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Fatigue Behaviour of Glass Fibre Reinforced Composites for Ocean Energy Conversion Systems


A Boisseau, P Davies F Thiebaud – Applied Composite Materials, February 2012

Abstract
The development of ocean energy conversion systems places more severe requirements on materials than similar land-based structures such as wind turbines. Intervention and maintenance at sea are very costly, so for ocean energy supply to become economically viable long term durability must be guaranteed. Cyclic loading is a common feature of most energy conversion devices and composites are widely used, but few data are available concerning the fatigue behaviour in sea water of composite materials. This paper presents the results from an experimental study to fill this gap. The fatigue behavior of composite materials reinforced with different types of glass fibre is characterized in air and in sea water; the influence of testing in sea water rather than air is shown to be small. However, sea water ageing is shown to reduce the fatigue lifetime significantly and strongly depends on matrix formulation.

 

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Filed under Materials and coatings, System Development