Reflectance spectra of Mesosiderites: Implications for asteroid 4 Vesta

Oxygen isotopic data argues that HEDs and mesosiderites may be from the same parent body. A spectral survey of mesosiderites was done to determine their spectral properties in the visible and near-infrared and compare to HEDs

Question words in pidgin and creole languages

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Reflexives

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Introduction

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Introduction : Problems in the identification of substratum features in the creole languages

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Conclusions

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Impact of wind conditions on thermal loading of PMSG wind turbine power converters

Power converter reliability is critical for permanent magnet synchronous generator (PMSG) wind turbines. Converter failures are linked to power module thermal loading but studies often neglect turbine dynamics, control and the impact of wind speed sampling rate on lifetime estimation. This paper addresses this using a 2MW direct-drive PMSG wind turbine model with a 2-level converter, and simulating junction temperatures (Tj) using a power module thermal equivalent circuit under various synthetic wind speed conditions. These synthetic wind conditions include constant and square wave profiles representing stable and gusty wind conditions. Responses to square wave wind speeds showed that the lower the gust frequency, the higher ∆Tj becomes, demonstrating that low turbulence sites have greater thermal variation in the converter. In contrast, wind speed variations with frequencies greater than 0.25Hz deliver only small increases in ∆Tj . It is concluded that reasonable approximations of Tj profiles can be made with 0.25Hz wind speed data, but that lower data rate wind measurements miss essential, damaging characteristics

Experimental Set-up for Applying Wind Turbine Operating Profiles to the Nacelle Power Converter

Studies have shown that the reliability of fully rated converters (FRC) in permanent magnet synchronous generator (PMSG) wind turbines is critical. This paper outlines an experimental rig that applies PMSG wind turbine specific operating profiles to a machine side converter (MSC) power module. A number of test regimes have been designed to verify thermal models of the power module, validate the use of cycle life vs. Tj profile manufacturing data, and determine the wind turbine operational profiles that cause the most damage to the MSC

Evaluation of Synthetic Wind Speed Time Series for Reliability Analysis of Offshore Wind Farms

A method for synthesising wind speed time series (WSTS) from limited data is required that can be used for reliability examination of wind farms and maintenance strategies for a range of wind speed scenarios. Key characteristics of the wind resource need to be captured, including energy availability and maintenance weather windows. 4 WSTS simulators were used to produce synthetic WSTS based on benchmark data from a meteorological mast data at the offshore Egmond aan Zee wind farm in the Netherlands. These synthetic WSTS were compared with test criteria to determine their suitability for reliability analysis. This included comparing the synthetic WSTS to the benchmark data in terms of the energy availability in the wind and from a typical turbine, residence time at wind speeds, number of transitions between 1m/s wind speed bins, replication of seasonal characteristics including weather windows, and underlying statistical properties. Based on the chosen criteria, the most appropriate WSTS simulator was the modified Markov process. However, no modelling technique performed best against all criteria and none capture the autocorrelation function (ACF) as closely as desired. Therefore, there is scope for a more advanced technique for wind speed modelling for reliability analysis which combines the best aspects of the models used in this work