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Vaheeshan J.,University of Peradeniya | Vihirthanath V.,University of Peradeniya | Abeyaratne S.G.,University of Peradeniya | Atputharajah A.,University of Peradeniya | Ramatharan G.,Garrad Hassan and Partners Ltd
2011 6th International Conference on Industrial and Information Systems, ICIIS 2011 - Conference Proceedings | Year: 2011

The paper presents the development of a DC motor based Wind Turbine Emulator (WTE) and its performance verification through simulation. The torque signal that represents the actual wind turbine with environmental effect was made to generate at the DC motor shaft. Particularly, the study incorporates the turbine power control strategy including the effect of stochastic and deterministic load components with the shaft dynamics. The WTE with the Wind Energy Conversion System (WECS) is studied to verify the effectiveness of the WTE in the presence of various wind characteristics. © 2011 IEEE.


Arulampalam A.,University of Peradeniya | Ramtharan G.,Garrad Hassan and Partners Ltd | Ekanayake J.B.,University of Cardiff | Tennakoon A.P.,Ceylon Electricity Board | And 2 more authors.
2010 5th International Conference on Industrial and Information Systems, ICIIS 2010 | Year: 2010

The electromechanical transients during a deloading of a DFIG turbine and the Fault Ride Through (FRT) capability of a DFIG wind farm connected through HVDC transmission lines are discussed. The electromechanical oscillations during a deloading operation of a DFIG wind turbine generator are simulated using BLADED software. Then power reduction control during a fault was achieved by reducing the power from the wind farm as a whole and by deloading the individual wind generator. A new power blocking technique applied at the offshore converter station was used to reduce the wind farm power output. Simultaneous control of the wind farm and wind turbine power outputs enabled a smooth power reduction during the fault. ©2010 IEEE.


Manning J.,University of Surrey | Hancock P.,University of Surrey | Whiting R.,Garrad Hassan and Partners Ltd
Wind Engineering | Year: 2010

Comparisons are made between Meteodyn WT (MWT) and wind tunnel measurements from the three RUSHIL test cases that represent hills of increasing steepness. The two steeper cases are of interest; in one the flow on the lee side is close to separation (Hill 5), for the other the flow has clearly separated (Hill 3). Although it is well known that WAsP 8.3 (WP) cannot predict separation, its predictions are included to represent the current industry standard. Both models agree well with mean wind speeds measured upstream of the Hill 5 crest. MWT gives significantly better but not good agreement upstream of the Hill 3 crest, where WP significantly over-predicts the speed-up. Downstream, MWT predictions are closer to measurements, but predict a smaller separation bubble on Hill 3, due to limitations of the turbulence model. A practical viewpoint requires improved modelling to have only a minimal impact on computational resource requirements.


Bahaj A.S.,University of Southampton | Myers L.E.,University of Southampton | Rawlinson-Smith R.I.,Garrad Hassan and Partners Ltd | Thomson M.,Garrad Hassan and Partners Ltd
Journal of Offshore Mechanics and Arctic Engineering | Year: 2011

An experimental and theoretical investigation of the flow field around small-scale mesh disk rotor simulators is presented. The downstream wake flow field of the rotor simulators has been observed and measured in the 21m tilting flume at the Chilworth hydraulics laboratory, University of Southampton. The focus of this work is the proximity of flow boundaries (sea bed and surface) to the rotor disks and the constrained nature of the flow. A three-dimensional Eddy-viscosity numerical model based on an established wind turbine wake model has been modified to account for the change in fluid and the presence of a bounding free surface. This work has shown that previous axi-symmetric modeling approaches may not hold for marine current energy technology and a novel approach is required for simulation of the downstream flow field. Such modeling solutions are discussed and resultant simulation results are given. In addition, the presented work has been conducted as part of a UK Government funded project to develop validated numerical modeling tools which can predict the flow onto a marine current turbine within an array. The work feeds into the marine energy program at Southampton to assist developers with layout designs of arrays which are optimally spaced and arranged to achieve the maximum possible energy yield at a given tidal energy site. © 2012 American Society of Mechanical Engineers.


Caliao N.D.,Mindanao University of Science and Technology | Ramtharan G.,Garrad Hassan and Partners Ltd. | Ekanayake J.,University of Cardiff | Jenkins N.,University of Cardiff
Proceedings of the Universities Power Engineering Conference | Year: 2010

A power oscillation damping controller for fully rated converter wind turbines was investigated. Small signal analysis and time domain simulations were used to investigate the performance of the fully rated converter wind turbine with a power oscillation damping controller when connected to a single bus representation of the large power system. A power oscillation damping controller for fully rated converter wind turbines was shown to improve network damping. Simulation results also show that, with a power oscillation damping controller incorporated into the grid side converter of fully rated converter wind turbines, decoupling between the generator and grid is maintained.


Bossanyi E.,Garrad Hassan and Partners Ltd. | Wright A.,National Renewable Energy Laboratory | Fleming P.,National Renewable Energy Laboratory
European Wind Energy Conference and Exhibition 2010, EWEC 2010 | Year: 2010

An important task in the EU "UPWIND" project is to use field tests to demonstrate that the important load reductions predicted with individual pitch control (IPC) can really be achieved in practice. This is vital for increasing confidence of turbine designers to use IPC in their new designs, to improve cost-effectiveness. As well as reducing asymmetrical out of plane loading on three-bladed machines, IPC can also be used on two-bladed machines as an alternative to a mechanical teeter hinge. The NREL test site provides an excellent opportunity to test IPC on both the two-bladed (CART2) and three-bladed (CART3) turbines. At the same time, the efficacy of fore-aft tower damping (FATD) by means of collective pitch control will also be demonstrated. State-of-the-art control algorithms for both the CART2 and CART3 have been designed, including both IPC and FATD in addition to the normal speed regulation. The CART2 controller has been implemented on the turbine's control computer, and some early results have now been obtained. With no need for adjustments of any significance, the very first results already demonstrated good performance, as presented in this paper. The new CART3 controller has also been implemented on the control computer, but its use is awaiting the completion of turbine commissioning. First results for this turbine are now expected in late spring 2010.


Rogers K.,Garrad Hassan and Partners Ltd. | Collins J.,Garrad Hassan and Partners Ltd. | Parkes J.,Garrad Hassan and Partners Ltd. | Landberg L.,Garrad Hassan and Partners Ltd.
European Wind Energy Conference and Exhibition 2012, EWEC 2012 | Year: 2012

Short term forecasting of the production from wind farms for the purposes of grid integration, energy trading and optimising maintenance is well established in a number of countries around the world. However, with the rapidly increasing installed capacity offshore, a question that is often asked is: "What are the challenges of forecasting for offshore projects and is it more or less accurate than onshore?". This study aims to address this question. An explanation of the current best practises for short term forecasting is provided, in addition to a description of the major influences on forecast accuracy. The analysis was a UK-wide, intersite comparison. This investigation demonstrated that there were a number of factors affecting forecast accuracy, and that on average the forecast accuracies offshore and onshore were comparable. The best accuracy achievable was for onshore sites in flat terrain, the worst accuracy was for onshore sites in complex terrain, with offshore sites sitting somewhere in the mid range of accuracies. Whatever the location, good weather models and adaptable forecasting methods enable accurate forecasts to be generated, providing an essential tool for the efficient integration of wind energy into our electricity systems.


L. Mackay E.B.,Garrad Hassan and Partners Ltd. | Challenor P.G.,UK National Oceanography Center | Bahaj A.S.,University of Southampton
Ocean Engineering | Year: 2010

Extreme value theory is commonly used in offshore engineering to estimate extreme significant wave height. To justify the use of extreme value models it is of critical importance either to verify that the assumptions made by the models are satisfied by the data or to examine the effect violating model assumptions. An important assumption made in the derivation of extreme value models is that the data come from a stationary distribution. The distribution of significant wave height varies with both the direction of origin of a storm and the season it occurs in, violating the assumption of a stationary distribution. Extreme value models can be applied to analyse the data in discrete seasons or directional sectors over which the distribution can be considered approximately stationary. Previous studies have suggested that models which ignore seasonality or directionality are less accurate and will underestimate extremes. This study shows that in fact the opposite is true. Using realistic case studies, it is shown that estimates of extremes from non-seasonal models have a lower bias and variance than estimates from discrete seasonal models and that estimates from discrete seasonal models tend to be biased high. The results are also applicable to discrete directional models. © 2010 Elsevier Ltd. All rights reserved.


Cruz J.,Garrad Hassan Iberica S.L.U | Sykes R.,Garrad Hassan and Partners Ltd. | Siddorn P.,University of Oxford | Taylor R.E.,University of Oxford
IET Renewable Power Generation | Year: 2010

Estimates regarding the assessment of the energy absorption characteristics of an array of wave energy converters (also referred to as a wave farm) are presented. Regular and irregular waves are used as input in a frequency-domain hydrodynamic model, which allows iterations in the array layout and farm control strategy. Under such an approach each array element can be controlled independently while keeping the design objective (maximisation of the wave farm energy yield). The distribution of power take-off (PTO) loading on the various array elements, as induced by the incoming sea, is also investigated. The approach is verified by comparing the estimates with results from a semi-analytic method developed at the University of Oxford. The overall objective of the study is to quantify the influence of the array layout and farm control in the performance of a wave farm under the action of irregular waves. The results show that the energy yield and the PTO loads are affected by such factors; hence these can be seen as key design drivers in order to reduce the uncertainty and thus the cost of energy when planning a wave farm. Further studies may address additional constraints, either technical or economical. This study is expected to contribute to the development of specific modules of a design optimisation tool for wave farms, and extends the findings originally presented at the Eighth European Wave and Tidal Energy Conference. © 2010 © The Institution of Engineering and Technology.


Matha D.,University of Stuttgart | Schlipf M.,University of Stuttgart | Cordle A.,Garrad Hassan and Partners Ltd. | Pereira R.,Germanischer Lloyd Industrial Services | Jonkman J.,National Renewable Energy Laboratory
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

This paper presents the current major modeling challenges for floating offshore wind turbine design tools. It also describes aerodynamic and hydrodynamic effects due to rotor and platform motions and usage of non-slender support structures. The applicability of advanced potential flow and computational fluid dynamics-based aerodynamic and hydrodynamic simulation methods to represent these effects-exceeding state-of-the-art design tool capabilities-is analyzed and the results are presented. Different techniques for the representation of mooring-line dynamics, including quasi-static, finite element, and multibody methods, and their impact on global system loads are investigated. Conclusions are drawn about the importance of the relevant effects, strengths and weaknesses of the different methods are discussed, and development needs of future tools are described. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

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