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Online ISSN 1752-1424 Print ISSN 1752-1416

IET Renewable Power Generation

Volume 2, Issue 1, March 2008

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Volume 2, Issue 1

March 2008

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  • Selected papers from the European Wind Energy Conference (EWEC) 2007

    • Editorial: Selected papers from the European Wind Energy Conference (EWEC) 2007
      Structural mass in direct-drive permanent magnet electrical generators
      • Author(s): A.S. McDonald ; M.A. Mueller ; H. Polinder
      • Source: IET Renewable Power Generation, Volume 2, Issue 1, p. 3 –15
      • DOI:  10.1049/iet-rpg:20070071
      • Type: Article
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      • p. 3 –15 (13)
        Direct-drive permanent magnet (PM) synchronous machines for wind turbines are large, heavy and thus expensive to build, transport and install. The structure that is required to maintain the airgap clearance is often heavier than the electromagnetically active material. It is shown that the structural material can be estimated early on in the design process for axial-flux and radial-flux machines. By moving to a design without iron in the stator, the forces that the machine structure must deal with can be significantly reduced. The mass of iron-cored and air-cored axial-flux PM synchronous machines for a range of multi-MW wind turbines is compared. Scaling laws for PM generators in direct-drive wind turbines are also developed.
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      Analytical determination of steady-state converter control laws for wind turbines equipped with doubly fed induction generators
      • Author(s): D. Aguglia ; P. Viarouge ; R. Wamkeue ; J. Cros
      • Source: IET Renewable Power Generation, Volume 2, Issue 1, p. 16 –25
      • DOI:  10.1049/iet-rpg:20070042
      • Type: Article
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      • p. 16 –25 (10)
        An analytical method for the determination of the steady-state control laws of the doubly fed induction generators (DFIG) used in wind turbines is presented. The analytical model is used to derive the converter control laws of the generator in terms of rotor voltage and control angle (real and reactive power) on the whole operation speed range. The method can be efficiently implemented in a global optimisation CAD environment to design the converters and the generator associated to a given wind turbine. It is used to present some DFIG performances for different grid specifications and discuss the relative size of the rotor and grid side converters for a fixed induction generator and a given wind turbine of 2.5 MW.
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      Concepts for the improved integration of wind power into the German interconnected system
      • Author(s): P. Siemes ; H.-J. Haubrich ; H. Vennegeerts ; S. Ohrem
      • Source: IET Renewable Power Generation, Volume 2, Issue 1, p. 26 –33
      • DOI:  10.1049/iet-rpg:20070072
      • Type: Article
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      • p. 26 –33 (8)
        The ongoing increase in wind power in Germany requires the accomplishment of a number of challenges. Most notably, the substantial strain on the transmission grid and the increasing requirement of control reserve capacity need to be tackled. Therefore the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety has commissioned a scientific study, in which novel concepts for optimised integration of wind energy into the German interconnected system are being evaluated. The Institute of Power Systems and Power Economics (IAEW) of RWTH Aachen University and the Research Centre for Electrical Systems and Power Economics cooperatively handles the study. The investigations carried out by IAEW are focused. They comprise a generation management (GM) of wind turbines and an improvement in load forecast, both in terms of a reduction in necessary control reserve, an improved integration of wind power because of the utilisation of intraday markets, a demand-side management in order to provide control reserve and the potentials of modern storage technologies. Primarily, the application of GM proves to be of significant economical benefit. Moreover compressed air energy storages may prove to be a suitable utility for the integration of wind power.
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      Integration of large-scale wind power and use of energy storage in the Netherlands' electricity supply
      • Author(s): B.C. Ummels ; E. Pelgrum ; W.L. Kling
      • Source: IET Renewable Power Generation, Volume 2, Issue 1, p. 34 –46
      • DOI:  10.1049/iet-rpg:20070056
      • Type: Article
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      • p. 34 –46 (13)
        The use of energy storage for increased operational flexibility is commonly regarded as a logical complement for systems with large amounts of wind power. The authors explore, the opportunities for energy storage for the integration of large-scale wind power into a future lay-out of the Dutch generation system, for which minimum-load problems are foreseen with high wind power penetrations. A central unit commitment and economic despatch model is extended with models for three large-scale energy storage technologies: pumped hydro accumulation storage (PAC), underground PAC and compressed air energy storage. Furthermore, an alternative solution is investigated, comprising the installation of heat boilers at selected combined heat and power locations (CHP) in order to increase the operational flexibility of these units. Results are shown for different wind power penetrations and scenarios. A cost–benefit analysis shows that the operation cost savings from energy storage increase with the amount of wind power installed. Taking into account the large investment costs, energy storage units are however unlikely to have a profitable exploitation. The installation of heat boilers at CHP locations is found to be more efficient and a promising solution for the integration of large-scale wind power in the Netherlands. A notable result is that for the Dutch system, the use of energy storage increases the system's overall CO2 emission levels because energy storage allows storing power from cheap coal plants for substitution of expensive gas during peak. Even though often proposed as a solution for wind power integration, energy storage in fact partly annuls CO2 emission savings by wind power.
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      Advanced grid requirements for the integration of wind farms into the Spanish transmission system
      • Author(s): A. Morales ; X. Robe ; M. Sala ; P. Prats ; C. Aguerri ; E. Torres
      • Source: IET Renewable Power Generation, Volume 2, Issue 1, p. 47 –59
      • DOI:  10.1049/iet-rpg:20070084
      • Type: Article
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      • p. 47 –59 (13)
        The main purpose of this paper is to present the grid requirements for the integration of wind farms into the Spanish Transmission System. In the particular case of voltage support capability, the Spanish Transmission System Operator (TSO), Red Eléctrica de España (REE) has defined a set of conditions to be met at the point of common coupling of a wind farm, not at terminals of a single wind turbine. A Verification, Validation, and Certification Procedure (VV&CP) to check compliance at terminals of a wind farm has been developed with the contribution and common agreement of all different wind power players and distribution system operators, leaded by the Spanish Wind Energy Association and supervised by REE. The VV&CP solves the problem defining a “Particular Procedure” based on testing or a “General Procedure” based on the simulation of the wind farm behaviour. It is the scope of Energy to Quality in this paper, to discuss and confirm the VV&CP reliability and validity, supported by field testing, validated models of wind turbines and simulation of wind farms. Conclusions are drawn on our efforts towards worldwide harmonization, on the development of a common VV&CP based on the Spanish and German experience.
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      Condition monitoring benefit for onshore wind turbines: sensitivity to operational parameters
      • Author(s): D. McMillan  and  G.W. Ault
      • Source: IET Renewable Power Generation, Volume 2, Issue 1, p. 60 –72
      • DOI:  10.1049/iet-rpg:20070064
      • Type: Article
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      • p. 60 –72 (13)
        The economic case for condition monitoring (CM) applied to wind turbines is currently not well quantified and the factors involved are not fully understood. In order to make more informed decisions regarding whether deployment of CM for wind turbines is economically justified, a refined set of probabilistic models capturing the processes involved are presented. Sensitivity of the model outputs with respect to variables of interest are investigated within the bounds of published data and expert opinion. The results show that the levels of benefit are dependent on a variety of factors including wind profile, typical downtime duration and wind turbine sub-component replacement cost.
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