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Llorente Iglesias R.,European Commission | Lacal Arantegui R.,European Commission | Aguado Alonso M.,Renewable Energy National Center CENER
Renewable and Sustainable Energy Reviews | Year: 2011

The aim of the paper is to analyse the evolution of wind turbine concepts or topologies with a specific focus on their power electronics content, and to demonstrate the tendency of wind turbine manufacturers towards the development of generators connected to the grid by means of power electronics converters. The paper provides a review of the power electronics converters used in wind turbines and a briefer description of the components that make up those converters. Then the research, supported by a market study based on 91% of the total installed wind capacity during the period 2000-2009, demonstrates the evolution of the wind turbine market towards the use of power electronics converters with their market share increasing from 38% in 2000 to 80% in 2009. In particular, the type D wind turbine configuration - containing a full power converter - appears set up to increase market share in the next five years. If projections of these findings are realised wind turbines without a power converter could be reduced to a niche market as soon as 2013. The paper refers these findings to, among other reasons, the increasingly more strict technical requirements of the grid operation codes. Finally, the paper details some of the current research and development trends plus a vision of the future by the industry. © 2011 Elsevier Ltd. All rights reserved. Source

Sallaberry F.,Renewable Energy National Center CENER | Pujol-Nadal R.,University of the Balearic Islands | Martinez-Moll V.,University of the Balearic Islands | Torres J.-L.,Public University of Navarra
Renewable Energy | Year: 2014

Concentrating solar collectors are mentioned in the International Standards, but the general testing methods for solar collectors mentioned cannot easily be applied to such unusual collector designs. In this study, the best optical and thermal model for a variable geometry solar concentrator has been investigated. In the particular case of a collector with a fixed mirror concentrator, the relative position of the receiver with respect to the reflector is not constant during the day, and this variable geometry is not taken into account in the current testing Standards. An optical characterization of the prototype using a ray-tracing program has been performed, and the results have been used as an initial hypothesis to define two thermal models adapted from the European Standard. Those two different models have been compared. The optical results obtained from experiments have been compared to ray-tracing simulation results, and they have been found to be quite similar, considering the measurement uncertainties. This validation procedure of the optical simulation could be an important point to be taken into account in a future Standard revision for variable geometry collector types for which the normal incidence is not easy to obtain. © 2014 Elsevier Ltd. Source

Ferreira H.L.,TU Eindhoven | Garde R.,Renewable Energy National Center CENER | Fulli G.,European Commission | Kling W.,TU Eindhoven | Lopes J.P.,University of Porto
Energy | Year: 2013

In the current situation with the unprecedented deployment of clean technologies for electricity generation, it is natural to expect that storage will play an important role in electricity networks. This paper provides a qualitative methodology to select the appropriate technology or mix of technologies for different applications. The multiple comparisons according to different characteristics distinguish this paper from others about energy storage systems.Firstly, the different technologies available for energy storage, as discussed in the literature, are described and compared. The characteristics of the technologies are explained, including their current availability. In order to gain a better perspective, availability is cross-compared with maturity level. Moreover, information such as ratings, energy density, durability and costs is provided in table and graphic format for a straightforward comparison. Additionally, the different electric grid applications of energy storage technologies are described and categorised. For each of the categories, we describe the available technologies, both mature and potential. Finally, methods for connecting storage technologies are discussed. © 2013 Elsevier Ltd. Source

Iribas-Latour M.,Renewable Energy National Center CENER | Landau I.-D.,CNRS GIPSA Laboratory
Wind Energy | Year: 2013

To achieve load reduction and power optimization, wind turbine controllers design requires the availability of reliable control-oriented linear models. These are needed for model-based controller design. Model identification of wind turbine while operating in closed loop is an appropriate solution that has recently shown its capabilities when linear time-invariant controllers and complicated control structures are present. However, the collective pitch control loop, one of the most important wind turbine loops, uses non-linear controllers. Typically, this non-linear controller is a combination of a linear controller and a gain scheduling. This paper presents a new algorithm for identification in closed-loop operation that allows the use of this kind of non-linear controllers. The algorithm is applied for identification the collective pitch demand to generator speed of a wind turbine at various operating points. The obtained models are presented and discussed from a control point of view. The validity of these models is illustrated by their use for the design of a linear fix robust controller. The performance based on simulation data of this linear controller is similar to that obtained with simulations based on a linear controller with gain scheduling, but its design and implementation is much simpler. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd. Source

Yang W.,Northumbria University | Court R.,Renewable Energy National Center CENER
Measurement: Journal of the International Measurement Confederation | Year: 2013

Bearings are critical components in the products of many industries, and their failure can result in long downtime and costly maintenance. Prolonging a bearing's service in a safe manner is vital for operators of equipment, and condition monitoring is regarded as one of the best approaches to achieve this. In general practice, condition monitoring does successfully indicate the presence and growth of bearing faults. However, standard condition monitoring techniques do not usually have a proven method to determine the best time to conduct maintenance of a defective bearing. Traditionally, maintenance will be conducted when the measured vibration of a bearing is found to exceed an acceptable vibration level, as defined by an industry standard. However, the industry standard is only a general guideline to the design and operation of the kind of machines/components under certain conditions. The actual dynamic response of a bearing is reliant on a variety of factors, such as lubrication, loading, temperature, and operational and environmental conditions. As a consequence, although the empirical vibration levels suggested by the standard are helpful in ensuring the safe operation of a bearing, they cannot guarantee full utilization of the residual life of a defective bearing. The purpose of this paper is to try and find a feasible solution for this issue, and moreover validate it through a number of experiments conducted under various loading and operational conditions. In the research, four dimensionless condition monitoring criteria: normalized information entropy; J-Divergence; Kurtosis; and a composite criterion based on them, are employed to assess the actual health condition of the test bearings with different types and severity levels of failures. Experimental results have shown that in comparison of the industry standard, the proposed method provides an effective and feasible approach for predicting the optimum time to conduct bearing maintenance. It is deemed that the achievements of this work will help operators in further improving their management of assets. © 2013 Elsevier Ltd. All rights reserved. Source

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