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Sökning: db:Swepub > Fritt online > Licentiatavhandling > (1990-1994)

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  • Andersson, Kent (författare)
  • Preparation and Characterisation of Sputtered Titanium- and Zirconium Nitride Optical Films
  • 1993
  • Licentiatavhandling (övrigt vetenskapligt)abstract
    • Multilayered interference coatings based on titanium- and zirconium nitride and designed for solar control have been prepared using reactive d c magnetron sputtering. Preparation effects and degradation mechanisms were investigated. It was shown that the quality of the nitride strongly depends on the degree of crystallinity in the underlying oxide. It has been shown that the nitride layer partly oxidizes as the top oxide layer is deposited. The degradation is enhanced with temperature. A thin sacrificial layer of aluminium deposited between successive depositions of nitride and oxide is shown to improve the optical performance of the coating as preparedm as well as after accelerated ageing tests.The optical properties of opaque and semitransparent films of zirconium nitride have been studied. A thorough investigation of the influence of composition, deposition rate, substrate temperature and film thickness on the optical response of the film was performed. Both photometric and ellipsometric methods were used to determine thicknesses and the optical constants at wavelengths ranging from 0.23 to 25 μm. The resulting values of n and k, in the wavelength intervals where these independent methods are applicable, have been shown to agree extremely well. The results so far indicate an even larger potential for zirconium nitride based solar control coatings as compared to the titanium nitride based.Access to optical constants derived from films of zirconium nitride of variable quality made multilayer modelling a powerful tool in the design and analysis of solar control coatings.
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  • Grauers, Anders, 1966- (författare)
  • Synchronous generator and frequency converter in wind turbine applications : system design and efficiency
  • 1994
  • Licentiatavhandling (övrigt vetenskapligt)abstract
    • This report deals with an electrical system for variable-speed wind power plants. It consists of a synchronous generator, a diode rectifier and a thyristor inverter. The aim is to discuss the system design and control, to model the losses and to compare the average efficiency of this variable-speed system with the average efficiency of a constant-speed and a two-speed system. Only the steady state operation of the system is discussed. Losses in the system are modelled, and the loss model is verified for a 50 kVA generator. The proposed simple loss model is found to be accurate enough to be used for the torque control of a wind turbine generator system. The most efficient generator rating is discussed, and it is shown how the voltage control of the generator can be used to maximize the generator and converter efficiency. The average efficiency of the system is calculated. It depends on the median wind speed of the turbine site. It is found that a variable-speed system, consisting of a generator and a converter, can have an average efficiency almost as high as a constant-speed or a two-speed system. Three different control strategies and their effect on the system efficiency are investigated.
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