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| 2. |
- Fischer, Katharina, 1979, et al.
(författare)
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Field-Experience Based Root-Cause Analysis of Power-Converter Failure in Wind Turbines
- 2015
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Ingår i: IEEE Transactions on Power Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 30:5, s. 2481-2492
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Tidskriftsartikel (refereegranskat)abstract
- The frequent power-converter failure experienced in wind turbines has a strong economic impact through both the related turbine unavailability and the maintenance cost. Up to now, the prevailing mechanisms and causes underlying the converter failure in wind turbines are mostly unknown. Their identification is, however, a prerequisite for the development of effective solutions. This paper describes a multitrack empirical approach to failure analysis including systematic field-data evaluation, exploration of the real converter operating environment, and postoperational laboratory investigation of converter hardware. The analysis is carried out for two widely used multi-MW wind turbines with low-voltage, insulated-gate bipolar transistor-based converters (topology 1: doubly fed induction generator with partially rated converter, topology 2: induction generator with fully rated converter). The findings suggest that the principle failure mechanisms of power electronics found in other applications, namely solder degradation and bond-wire damage, play a minor role in the investigated types of wind turbines. Instead, the analysis reveals indications of insufficient protection of the converter hardware against the environment (salt, condensation, and insects) as well as indications of electrical overstress.
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| 3. |
- Haghbin, Saeid, 1977, et al.
(författare)
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An LCL filter with an active compensation for a fast charger station
- 2017
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Ingår i: IEEE International Conference on Environment and Electrical Engineering and 2017 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe). - 9781538639160
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Konferensbidrag (refereegranskat)abstract
- For the AC/DC stage of a 50 kW fast charger station which is a three-phase pulse width modulated (PWM) converter, an LCL filter is designed and constructed. As a PWM converter, the rectifier is a source of high frequency harmonics demanding filtering action to meet the grid regulations. Hence, the required filtering specification by the LCL filter is extracted using an appropriate harmonic model of the converter. The design procedure and the filter transfer function are presented. In addition, an active compensator is proposed to enhance the converter power factor by modification of the reference q current. Some simulation results are provided to show the effectiveness of the filter.
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| 4. |
- Haghbin, Saeid, 1977, et al.
(författare)
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The Design and Construction of Transformers for a 50 kW Three-Phase Dual Active Bridge DC/DC Converter
- 2018
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Ingår i: IEEE Vehicle Power and Propulsion Conference (VPPC). - 9781538613177
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Konferensbidrag (refereegranskat)abstract
- Fast charger stations are one of the key components towards more electric transport systems. The size and cost of high power chargers are demanding more improvement while a high level of efficiency are required. Consequently, the main methodology to achieve these specifications is to increase the system operating frequency, if the losses in the magnetic materials and semiconductors can handle that. A 50 kW compact and efficient fast charger station is designed and constructed in Chalmers University of Technology, Sweden. The charger structure is an active three- phase PWM converter followed by a three-phase dual active bridge DC/DC converter. The SiC high-power modules and nanocrystalline magnetic materials are utilized to achieve a higher frequency operating point. Three single-phase Y-Y connected transformers are are designed, constructed and partially verified in the circuit in which the leakage inductance of the transformers are used as the energy storage devices. Design considerations as well as simulation and measurement results are presented in this paper. The maximum error between the calculated, simulated and measured values is less than 2.5 %.
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| 5. |
- Karlsson, Per Erik, et al.
(författare)
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The vulnerability of northern European vegetation to ozone damage in a changing climate An assessment based on current knowledge
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The potential vulnerability of vegetation at northern latitudes to ozone damage was assessed based on current knowledge with regard to air ozone concentrations and leaf ozone uptake as well as to plant traits affecting ozone tolerance. The focus was on the northern European arctic, alpine and northern boreal vegetation zones, with a special focus on high-altitude vegetation. In particular, we analysed if there are increasing risks for ozone impacts on northern vegetation due to high spring ozone concentrations in relation to climate change induced shifts such as e.g. an earlier start of the growing season. The ozone concentrations in these regions are characterized by the influence of a combination of conditions caused by high latitudes and high altitudes. Ozone concentrations increase with altitude and the difference in ozone concentrations between day and night are smaller at high-altitude and high-latitude sites. Summer periods with long daylight conditions potentially promote the leaf ozone uptake through the open stomata. The aims of this report were: • To assess the current state of knowledge regarding the potential vulnerability of far northern vegetation to ozone damage, today and in the future • To provide advice for policy implications regarding necessary ozone precursor emission abatement • To provide advice for future research and monitoring of ozone impacts on the vegetation at northern latitudes Ongoing environmental changes affecting far northern latitude ecosystems were reviewed. Current and novel methods were described for how to estimate the time of year during which the ozone exposure for vegetation should be accumulated. Time trends for ozone concentrations at northern latitudes were analysed. Ozone episodes with high concentrations at far northern latitudes were described. Source attributions of northern ozone concentrations were analysed. Environmental conditions at far northern latitudes that might be important for ozone damage were evaluated. Plant traits that can influence the ozone vulnerability were discussed. Current experimental results for ozone injury on northern plant species were evaluated. Future scenarios for ozone impact on northern vegetation were discussed. Some important results from the analyses are described below. At high altitudes and high latitudes, the ozone concentrations are relatively similar during day- and night-time. Furthermore, at high latitudes, the long daylight duration during the summer has the potential to increase the duration of the daily period with plant gas exchange and leaf ozone uptake. Therefore, the absorption of ozone through the stomata may potentially be higher at northern latitudes. However, measurements of light intensity and quality at northern sites in combination with a simple calculation example illustrated that this probably was not the case, since the potential added ozone uptake in the early morning and late evening at northern sites may be cancelled out by a lower ozone uptake in the middle of the day, as compared to southern sites. Both data on budburst and data on ecosystem CO2 exchange as well as meteorological observations show that there has been a development towards an earlier start of the growing season during the year, with approximately 0.5 – 1 day per year. Thus, there is clear evidence for an earlier start of the growing season, which is likely to continue. However, the timing of the spring ozone maximum is also shifted towards earlier in the year. There is presently no evidence for an increasing overlap between the growing season and the ozone peak. Despite this, there is a potential for increased ozone uptake to vegetation in spring due to the earlier growing start of vegetation and increased uptake of ozone to vegetation in May. The impact of this on the accumulated phytotoxic ozone dose for northern vegetation needs to be investigated further. The overall conclusions about the present and near future ozone vulnerability of northern vegetation were: • There remain uncertainties regarding to what extent northern vegetation is affected by ozone exposure. • According to current knowledge, we could not find evidence that expected changes in ozone concentrations and climate would make the northern arctic, alpine and subalpine vegetation substantially more vulnerable to ozone than other types of European vegetation. • The risk of significant and lasting negative impact of the current exposure to ozone on northern boreal forests is most likely not greater than for boreonemoral and nemoral forests in southern Fennoscandia. • However, peak ozone concentrations occurring in spring and early summer may affect vegetation at northern latitudes in Fennoscandia since the start of the growing season in the future may occur earlier during the year. The policy implications that can be derived from these conclusions were: • The current state of knowledge implies that ecosystems in the far north are not more susceptible to ozone than vegetation in other parts of Europe. Hence, we cannot advocate for a stronger reduction of ozone precursors emissions based exclusively on the ozone sensitivity of vegetation in the far north. • Policies designed to reduce emissions of ozone precursors to protect vegetation in other parts of Europe as well as in the entire northern hemisphere are likely to suffice to protect vegetation in northern Fennoscandia. There are important remaining knowledge gaps. Our conclusions are based on important, but limited observations. Experimental evidence from investigations specifically designed to study ozone sensitivity of high-altitude vegetation in northern Europe are to a large extent lacking. It is recommended that further experimental research is undertaken to directly compare the ozone sensitivity of plants of high-latitude/high-altitude origin with that of plants (species, genotypes) representative of regions of the southern part of the Nordic region. This research should include the characteristics of the high-latitude climate and other conditions. A specific research question is if the new ozone critical levels for European vegetation based on PODYSPEC (Mapping Manual, 2017) are correct, both regarding calculation methodology as well as impact assessments? In particular, there is a lack of information about the degree of stomata closure during nights in high-latitude area plants. This is important for the modelling of ozone uptake (dry deposition) in these areas and requires coordinated measurement campaigns in close cooperation with modelers. Further research questions may be related to the future development of the northern regions – e.g. oil and gas extraction including flaring, shipping, more tourism and climate change – how will that affect the ozone exposure of in the northern vegetation? Do future ozone precursor emission scenarios describe this correctly? Will warm and dry summers like 2018 become more frequent in connection with climate change, and how will this affect ozone impacts on vegetation? There are currently very few, long term ozone monitoring stations in the arctic and alpine vegetation zones, in particular at high altitudes. Given the expected increase in anthropogenic activities in these areas in combination with climate change, it is strongly recommended to increase the number of high-altitude ozone monitoring sites in these regions.
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| 6. |
- Lundell, Anna-Carin, 1976, et al.
(författare)
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High circulating immunoglobulin A levels in infants are associated with intestinal toxigenic Staphylococcus aureus and a lower frequency of eczema.
- 2009
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Ingår i: Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology. - : Wiley. - 1365-2222. ; 39:5, s. 662-70
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Intestinal bacteria trigger IgA production and delayed maturation of mucosal IgA response is linked to allergy development. OBJECTIVE: Our aim was to investigate if plasma levels of IgA or APRIL (a proliferation inducing ligand), an important factor for IgA class switch recombination, in infancy correlates with intestinal colonization by any specific bacteria or yeast. We also examined if plasma IgA or APRIL levels are related to sensitization and the development of eczema. METHODS: IgA was quantified in plasma obtained from infants at birth and at 4 and 18 months of age and APRIL was measured at 4 months of age. Colonization by major bacterial groups and yeast was followed in the first 8 weeks of life by quantitative culture of stool samples. A clinical evaluation regarding the presence of allergen-specific IgE or eczema and eosinophil counts in blood was performed at 18 months of age. RESULTS: In multiple linear regression analysis, only colonization by Staphylococcus aureus strains producing toxins with superantigen function (SEA-D or TSST-1) made an independent contribution to plasma IgA levels at 4 months of age. Further, increased levels of APRIL in plasma at 4 months were negatively associated with sensitization while IgA plasma levels were inversely correlated to eczema development and blood eosinophil counts at 18 months of age. CONCLUSION: Early intestinal colonization by toxigenic S. aureus strains seems to promote systemic IgA responses. Furthermore, high levels of APRIL and IgA in the circulation at 4 months of age seem to correlate negatively with allergy development.
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| 7. |
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| 8. |
- Palmberg, Eva, 1939, et al.
(författare)
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Wireless Charging for vehicles-Some Key Elements
- 2014
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Ingår i: 2014 16th European Conference on Power Electronics and Applications (EPE'14-ECCE Europe), Lappeenranta, Finland, 26-28 August 2014. - 2325-0313. - 9781479930159
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Konferensbidrag (refereegranskat)abstract
- In this paper so called wireless charging is investigated, primarily considering applications such as charging hybrid or electric vehicles at stand-still. The base concept investigated is a sending and a receiving coil at various designs. The theory behind wireless energy transfer and the needed components are described and analyzed, showing how design aspects, frequencies, height and vertical displacement affect the results. Analytical expressions, measurements, as well as FEM analyses in 2D and 3D with two different FEM programs have been compared, with a reasonable agreement between methods.
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| 9. |
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| 10. |
- Palmberg, Eva, 1939, et al.
(författare)
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Wireless charging using a resonant auxiliary winding
- 2015
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Ingår i: 2015 10th International Conference on Ecological Vehicles and Renewable Energies, EVER 2015. - 9781467367844
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Konferensbidrag (refereegranskat)abstract
- In this paper wireless charging using a resonant auxiliary winding is evaluated, showing that a substantial increase of the power level is possible with the extra winding. The coils have been evaluated theoretically and by means of FEM-analysis. Further on verification has been done on a laboratory 6 kW-charger. The charger has been used for charging the battery of a small test vehicle.
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