| 1. |
- Carlson, Ola, 1955, et al.
(författare)
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Power System Voltage Stability Related to Wind Power Generation
- 2006
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Ingår i: 2006 European Wind Energy Conference and Exhibition, Athens, Greece.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- As is well known the amount of installed wind power increases every day. In the past single wind turbines were installed separately, today wind turbines often are connected to the grid as a group of many turbines, i.e. wind parks. Grid integration considerations have moved from flicker phenomena in the low voltage grid to voltage stability analyses in the transmission grid. This paper starts with an overview of the voltage stability phenomena in a transmission system. Suitable models of wind power generation for power system stability studies - both long and short-term stability - are presented. Different levels of detail of the wind generation models are investigated carefully considering the type of stability study, result accuracy and simulation efficiency. Important aspects such as protection, fault ride-through capability and the capability of producing reactive power are taken into account. The models are then validated against measurements.Three types of wind turbines are considered in this study; fixed speed with induction generator, variable speed operation with doubly fed induction generator and variable speed turbine with full power converter.The main phenomenon that determines the behaviour of a system where fixed speed wind turbines are connected is the large reactive power consumed by the induction machines immediately after the fault has been cleared. This mechanism leads to a voltage stability problem with a risk of voltage collapse as a final consequence. Investigations in short and long term voltage stability have examined the factors affecting the stability limit such as: generated power, fault types, fault duration, fault clearing time, fault voltage and remaining voltage. Variable speed wind turbines with power electronic converter are capable of producing active power at unity power factor. Possibility lies to control reactive power during grid disturbance with the help of an over-rated grid side converter. In this paper the long- and short-term voltage stability aspects of variable speed wind turbines with power electronic converters are illustrated by case studies. Large scale wind power integration at the transmission level has the possibility to improve long term voltage stability of the grid by injecting reactive power. The possibility to produce reactive power increases with a decreased active power production. As well small scale integration at the distribution level can increase short-term voltage stability of the local grid by utilizing its fast reactive power control capability.Finally, several issues related to the modelling and the compatibility of wind power generation in typical power system simulation tools is discussed.
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| 2. |
- Martins, Marcia, 1966, et al.
(författare)
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Validation of fixed speed wind turbine dynamic models with measured data
- 2007
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 32:8, s. 1301-1316
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Tidskriftsartikel (refereegranskat)abstract
- Power system dynamics studies involving fixed-speed wind turbines normally use a wind turbine model consisting of two lumped masses, an elastic coupling and a induction generator model which neglects stator transients. However, validations of this model with measured data are rarely reported in the literature. This paper validates the model using a recorded case obtained in a fixed speed, stall regulated 180 kW wind turbine through a voltage dip. The work analyses the performance of the reduced order induction generator model which neglects stator transients, compared to the detailed induction generator model. It also includes a study of the convenience of representing mechanical damping in the drive train, and an evaluation of the single mass mechanical model.
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| 3. |
- Saxena, Richa, et al.
(författare)
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Genome-wide association analysis identifies loci for type 2 diabetes and triglyceride levels
- 2007
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 316:5829, s. 1331-1336
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Tidskriftsartikel (refereegranskat)abstract
- New strategies for prevention and treatment of type 2 diabetes (T2D) require improved insight into disease etiology. We analyzed 386,731 common single-nucleotide polymorphisms (SNPs) in 1464 patients with T2D and 1467 matched controls, each characterized for measures of glucose metabolism, lipids, obesity, and blood pressure. With collaborators (FUSION and WTCCC/UKT2D), we identified and confirmed three loci associated with T2D - in a noncoding region near CDKN2A and CDKN2B, in an intron of IGF2BP2, and an intron of CDKAL1 - and replicated associations near HHEX and in SLC30A8 found by a recent whole-genome association study. We identified and confirmed association of a SNP in an intron of glucokinase regulatory protein (GCKR) with serum triglycerides. The discovery of associated variants in unsuspected genes and outside coding regions illustrates the ability of genome-wide association studies to provide potentially important clues to the pathogenesis of common diseases.
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| 4. |
- Schmit, Stephanie L, et al.
(författare)
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Novel Common Genetic Susceptibility Loci for Colorectal Cancer.
- 2019
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Ingår i: Journal of the National Cancer Institute. - : Oxford University Press (OUP). - 0027-8874 .- 1460-2105. ; 111:2, s. 146-157
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Tidskriftsartikel (refereegranskat)abstract
- Background: Previous genome-wide association studies (GWAS) have identified 42 loci (P < 5 × 10-8) associated with risk of colorectal cancer (CRC). Expanded consortium efforts facilitating the discovery of additional susceptibility loci may capture unexplained familial risk.Methods: We conducted a GWAS in European descent CRC cases and control subjects using a discovery-replication design, followed by examination of novel findings in a multiethnic sample (cumulative n = 163 315). In the discovery stage (36 948 case subjects/30 864 control subjects), we identified genetic variants with a minor allele frequency of 1% or greater associated with risk of CRC using logistic regression followed by a fixed-effects inverse variance weighted meta-analysis. All novel independent variants reaching genome-wide statistical significance (two-sided P < 5 × 10-8) were tested for replication in separate European ancestry samples (12 952 case subjects/48 383 control subjects). Next, we examined the generalizability of discovered variants in East Asians, African Americans, and Hispanics (12 085 case subjects/22 083 control subjects). Finally, we examined the contributions of novel risk variants to familial relative risk and examined the prediction capabilities of a polygenic risk score. All statistical tests were two-sided.Results: The discovery GWAS identified 11 variants associated with CRC at P < 5 × 10-8, of which nine (at 4q22.2/5p15.33/5p13.1/6p21.31/6p12.1/10q11.23/12q24.21/16q24.1/20q13.13) independently replicated at a P value of less than .05. Multiethnic follow-up supported the generalizability of discovery findings. These results demonstrated a 14.7% increase in familial relative risk explained by common risk alleles from 10.3% (95% confidence interval [CI] = 7.9% to 13.7%; known variants) to 11.9% (95% CI = 9.2% to 15.5%; known and novel variants). A polygenic risk score identified 4.3% of the population at an odds ratio for developing CRC of at least 2.0.Conclusions: This study provides insight into the architecture of common genetic variation contributing to CRC etiology and improves risk prediction for individualized screening.
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| 5. |
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| 6. |
- Thomson, Elizabeth, et al.
(författare)
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Childbearing Across Partnerships in Australia, the United States, Norway, and Sweden
- 2014
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Ingår i: Demography. - : Duke University Press. - 0070-3370 .- 1533-7790. ; 51:2, s. 485-508
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Tidskriftsartikel (refereegranskat)abstract
- This article compares mothers' experience of having children with more than one partner in two liberal welfare regimes (the United States and Australia) and two social democratic regimes (Sweden and Norway). We use survey-based union and birth histories in Australia and the United States and data from national population registers in Norway and Sweden to estimate the likelihood of experiencing childbearing across partnerships at any point in the childbearing career. We find that births with new partners constitute a substantial proportion of all births in each country we study. Despite quite different arrangements for social welfare, the determinants of childbearing across partnerships are very similar. Women who had their first birth at a very young age or who are less well-educated are most likely to have children with different partners. The educational gradient in childbearing across partnerships is also consistently negative across countries, particularly in contrast to educational gradients in childbearing with the same partner. The risk of childbearing across partnerships increased dramatically in all countries from the 1980s to the 2000s, and educational differences also increased, again, in both liberal and social democratic welfare regimes.
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| 7. |
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| 8. |
- Thomson, Elizabeth, 1945-, et al.
(författare)
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Multiple-partner fertility in Europe and the United States
- 2020
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Ingår i: Analyzing Contemporary Fertility. - Cham : Springer Publishing Company. - 9783030485184 - 9783030485191 ; , s. 173-198
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Bokkapitel (refereegranskat)abstract
- In this chapter, we investigate what can be termed multi-partner fertility, i.e., the birth rate among women at risk of having a child with a new partner. We used data from 14 European countries and the United States, all with high-quality birth and union histories. We divided a woman’s exposure to the birth risk into three types – single spells up to and including the first birth, spells in a marital or cohabiting union up to and including the end of the first fertile union, and spells after a first non-union birth or after the end of the first fertile union. The last set of spells are those in which a woman is at risk of having a child with more than one partner. Age-specific fertility rates were estimated and combined to generate fertility rates for each union status across five decades in 14 European countries and the United States. We found that, with one exception, multi-partner fertility is quite modest, up to 9% of total fertility. In the United States, however, multi-partner fertility contributes more than 20% of total fertility. Countries with relatively high rates of non-union first births also have relatively high rates of multi-partner fertility. Multi-partner fertility is spread out across older ages, in comparison to single-partner fertility that peaks sharply in the early- to mid-20s. Although the exposure to risk of multi-partner fertility has increased over the decades observed, rates of multi-partner fertility have remained relatively stable.
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