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- Eriksson, Sandra, 1979-
(författare)
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Direct Driven Generators for Vertical Axis Wind Turbines
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wind power is a renewable energy source that is increasingly used all over the world. Most wind turbines have a horizontal axis of rotation but a few have a vertical axis of rotation. The concept presented in this thesis is a straight-bladed vertical axis wind turbine with a direct driven cable-wound permanent magnet synchronous generator. A comparison of the two different types of wind turbines, vertical axis wind turbines and horizontal axis wind turbines, have been performed considering several different aspects. However, the main focus in this thesis is on the generator. Several generators have been modelled with a combined field and circuit model, which has been solved by using the finite element method. A 12 kW generator has been designed, which has a high overall efficiency and a high overload capability. The generator has been constructed at the department and was tested in the laboratory before being mounted in a vertical axis wind turbine. Results from experiments correspond well with results from simulations. The generator has been tested for different loading conditions and the harmonic content of the voltage has been analysed. A 12 kW vertical axis wind turbine was completed and tests have been performed. The results are encouraging and further studies on the prototype will be performed in the future. The simulation method has been used to study electromagnetic losses in several generators. The comparison showed that the average losses should be considered when a variable speed generator for wind power is designed and it concluded that the design optimization process becomes a compromise between lowering the electromagnetic losses and having high overload capability. When constructing a wind turbine, it is important to consider vibrations in the structure. Torsional vibrations in the drive shaft connecting the turbine to the rotor of the generator have been studied. It is shown that a direct driven generator is to prefer over an induction generator with a gearbox when torsional vibrations are concerned. This thesis is based on eight papers all concerning vertical axis wind turbines with three of them focusing on the generator.
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| 2. |
- Ohlin, Andreas
(författare)
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Aspects on early diagnosis of neonatal sepsis
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents four studies, all designed to improve the problematic diagnostic situation concerning infants with suspected sepsis. Study I included 401 neonates with suspected sepsis. Nine signs of sepsis and C-reactive protein were prospectively recorded and logistic regression was used to assess associations between these signs and a subsequently confirmed diagnosis of sepsis. C-reactive protein and five of the clinical signs were statistically significantly associated with a positive bloodculture. When the material was stratified by gestational age, differences between premature and full term infants were detected.Studies II and III were prospective studies that used samples collected from neonates with suspected sepsis to evaluate a novel real-timepolymerase chain reaction (PCR) method. The results where compared with simultaneously collected blood cultures. Study II used plasma samples and resulted in a sensitivity of 42% and specificity of 95%. In study III, the protocol was improved and adapted to whole blood samples which resulted in a sensitivity of 79% and specificity of 90%. Both protocols included species-specific probes and study III indicated that PCR has the potential to detect bacteria in culture-negative sepsis.Staphylococcus epidermidis is the most common pathogen in neonatal sepsis, but there is still a lack of typing methods suitable for large materials of S. epidermidis. In Study IV we therefore evaluated a new S. epidermidisgenotyping method based on PCR for the repeat regions of four genes thatencode for cell wall anchoring proteins. The method was applied to 49well-defined neonatal blood isolates of S. epidermidis. The combination ofsdrF and aap seemed to be optimal, resulting in a diversity index of 0.92.Conclusions• Bradycardia, apnoea, low blood pressure, feeding intolerance and distended abdomen are obvious early signs of neonatal sepsis. Premature and full-term infants differ in terms of the signs they display in neonatal sepsis.• Blood is superior to plasma for developing PCR methods for bacterial DNA detection. The PCR method described in study III can detect neonatal bacteraemia, but it can be further improved before it is used in routine care.• There has been a lack of useful typing methods for S. epidermidis.We can now present PCR of the genes for the cell wall anchoring proteins sdrF and aap as a novel and feasible approach when there is a need to type a large number of S. epidermidis isolates.
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