| 11. |
- Magnusson, Jesper, 1984-, et al.
(författare)
-
On the Use of Metal Oxide Varistors as a Snubber Circuit in Solid-State Breakers
- 2013
-
Ingår i: 2013 4th IEEE/PES Innovative Smart Grid Technologies Europe, ISGT Europe 2013. - : IEEE. - 9781479929849 ; , s. 6695454-
-
Konferensbidrag (refereegranskat)abstract
- When solid-state switches are used in DC-breaker topologies, the turn-off operation can cause transient over-voltages that might harm the semiconductor itself. The over-voltage is caused by the combination of the very rapid current decrease of a solid-state switch and an undesired stray inductance in the parallel MOV-branch. The authors have proposed a possible solution where a smaller MOV is connected close to the solid-state switch to limit the over-voltage. This way, the over-voltage protection can be separated from the energy absorption task of the MOV. A small scale test set-up has been used to show that the peak voltage across the breaker is fully determined by the inner MOV. It is also shown that the performance can be increased by changing the U-I-characteristics of the outer MOV by adding several components in parallel.
|
|
| 12. |
- Magnusson, Jesper, 1984-, et al.
(författare)
-
Optimal design of a medium voltage hybrid fault current limiter
- 2014
-
Ingår i: 2014 IEEE International Energy Conference, ENERGYCON. - : IEEE Computer Society. - 9781479924493 ; , s. 431-438
-
Konferensbidrag (refereegranskat)abstract
- The connection of distributed generation increases the short circuit power which in turn might exceed the ratings of the installed circuit breakers. A solution is to limit the available short circuit power by increasing the grid impedance, but since there is a constant strive for lower losses and higher power transfer capabilities, this is not desired. The application of a fault current limiter (FCL) that can limit the current before the first peak enables a power system with high short circuit power and low short circuit current. This can increase the stability of the grid and reduce the requirements of other equipment. This work presents a simulation model to be used as an aid in the design of a hybrid FCL for a 12 kV AC system. The proposed model combines a transient analysis circuit model with an optimization module to obtain multiple sets of possible design parameters. The design is not straight forward since there is a trade-off between several of the design parameters.
|
|
| 13. |
- Magnusson, Jesper, et al.
(författare)
-
Separation of the energy absorption and overvoltage protection in solid-state breakers by the use of parallel varistors
- 2014
-
Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107. ; 29:6, s. 2715-2722
-
Tidskriftsartikel (refereegranskat)abstract
- Hybrid and solid-state breakers offer new possibilities in the power grid by enabling faster switching, and by simplifying dc breaking. However, they consists of expensive power electronic components that are sensitive to overvoltage transients and require energy absorbing elements mounted in parallel. At turn-off, the rapidly decreasing current in the power electronic switch and the presence of an inherent stray inductance leads to hazardous overvoltage transients across the breaker. This paper investigates the possibility to split the overvoltage protection and energy absorption into two separate components. By optimizing the voltage ratio between two varistors, one can dimension a small electronics varistor for overvoltage protection and a large power electronics varistor for energy absorption. With this setup the power electronics varistor is allowed to be in a circuit with a large stray inductance and can thus be placed further away without causing an uncontrolled overvoltage. It is shown both in circuit simulations as well as in a small-scale experiment that if the voltage ratio between the two varistors is large enough, the inner varistor only has to absorb 1-2% of the system energy.
|
|
| 14. |
- Magnusson, Jesper, et al.
(författare)
-
The Impact of Viral Respiratory Tract Infections on Long-Term Morbidity and Mortality following Lung Transplantation: A Retrospective Cohort Study Using a Multiplex PCR Panel.
- 2013
-
Ingår i: Transplantation. - 1534-6080. ; 95:2, s. 383-388
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The major factor affecting morbidity and mortality after lung transplantation (LTX) is bronchiolitis obliterans syndrome. Earlier studies have suggested a connection between the presence of viral agents and morbidity in this patient group, but data are somewhat conflicting. The objective of this study was to investigate the development of bronchiolitis obliterans syndrome and graft loss after LTX in relation to the presence of respiratory viruses during the first year after LTX. METHOD: The study is a retrospective cohort study of 39 LTX recipients 11-13 years after surgery. Patients were operated between January 1, 1998 and December 31, 2000 at Sahlgrenska University Hospital. The presence of virus in bronchoalveolar lavage (BAL) fluids from patients during the first year after surgery was analyzed retrospectively using a multiplex polymerase chain reaction test capable of detecting 15 respiratory agents. The time to BOS or graft loss was analyzed in relation to the positive findings in BAL during the first year after LTX. RESULTS: Patients with one or more viruses detected in BAL during the first year after transplantation demonstrated a significantly faster development of BOS (P=0.005) compared with patients with no virus detected. No significant difference in graft survival was found. CONCLUSION: Our results suggest that the long-term prognosis after LTX may be negatively affected by viral respiratory tract infections during the first year after LTX.
|
|
| 15. |
- van der Pals, J., et al.
(författare)
-
Hypothermia in cardiogenic shock reduces systemic t-PA release
- 2011
-
Ingår i: Journal of Thrombosis and Thrombolysis. - : Springer Science and Business Media LLC. - 0929-5305 .- 1573-742X. ; 32:1, s. 72-81
-
Tidskriftsartikel (refereegranskat)abstract
- Therapeutic hypothermia has been found to improve hemodynamic and metabolic parameters in cardiogenic shock. Tissue plasminogen activator (t-PA) is a pro-thrombolytic enzyme, which also possesses pro-inflammatory properties. Interleukin 6 (IL-6) and tumour necrosis factor alpha (TNF-alpha) are pro-inflammatory cytokines; interleukin 10 (IL-10) and transforming growth factor beta 1 (TGF-beta1) are anti-inflammatory cytokines. The aim of this experiment was to investigate the mechanism behind the protective effect of therapeutic hypothermia in cardiogenic shock. This was done by studying the effect of hypothermia on basal t-PA levels, peripheral t-PA release, and on the inflammatory response. Cardiogenic shock was induced by inflation of an angioplasty balloon in the proximal left anterior descending artery for 40 min in 16 pigs, followed by 110 min of reperfusion. The animals were randomized to hypothermia (33 degrees C, n = 8), or normothermia (n = 8) at reperfusion. Hemodynamic parameters were continuously monitored. Plasma was sampled every 30 min for analysis of blood-gases and t-PA, and for analysis of inflammatory markers at baseline and at the end of the experiment. t-PA, IL-6 and TGF-beta1 increased during cardiogenic shock. Apart from favourably affecting hemodynamic and metabolic variables, hypothermia was found to reduce basal arterial and venous t-PA levels, and to inhibit the release of t-PA from the peripheral vascular bed. Hypothermia did not alter the inflammatory response. In conclusion, mild hypothermia improves hemodynamic and metabolic parameters in cardiogenic shock. This is associated with a reduction in basal t-PA levels and t-PA release from the peripheral vascular bed, but not with an altered inflammatory response.
|
|
| 16. |
- Wallentin, Jesper, et al.
(författare)
-
Degenerate p-doping of InP nanowires for large area tunnel diodes
- 2011
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:25
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated p-doping of InP nanowires using diethyl zinc. Two-terminal devices showed non-linear source-drain characteristics and p-type gate dependence. Electron beam induced current measurements were employed to determine minority carrier diffusion lengths. We used large-area tunnel diodes to demonstrate degenerate doping, showing peak current densities of up to 0.11 A/cm(2) and room temperature peak to valley current ratios of 5.3. These results demonstrate that high p- and n-doping, paired with sharp doping profiles, can be achieved in InP nanowires. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3669697]
|
|
| 17. |
- Wallentin, Jesper, et al.
(författare)
-
InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit.
- 2013
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 339:6123, s. 1057-1060
-
Tidskriftsartikel (refereegranskat)abstract
- Photovoltaics based on nanowire arrays could reduce cost and materials consumption compared to planar devices, but have exhibited low efficiency of light absorption and carrier collection. We fabricated a variety of millimeter-sized arrays of p-i-n doped InP nanowires and found that the nanowire diameter and the length of the top n-segment were critical for cell performance. Efficiencies up to 13.8% (comparable to the record planar InP cell) were achieved using resonant light trapping in 180-nanometer-diameter nanowires that only covered 12% of the surface. The share of sunlight converted into photocurrent (71%) was six times the limit in a simple ray optics description. Furthermore, the highest open circuit voltage of 0.906 volt exceeds that of its planar counterpart, despite about 30 times higher surface-to-volume ratio of the nanowire cell.
|
|
