Transactions


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Performance of DFIG and PMSG Wind Turbines


Book Description

Due to environmental pollution and climate change, the use of renewable energy sources as an alternative means of power generation is on the rise globally. This is because of their clean nature, which makes them ecofriendly with little or no pollution compared to the traditional fossil fuel power-generation power plants. Among the various renewable energy sources, wind energy is one of the most widely employed, due to its promising technology. Wind turbine technologies could be classified into two groups as follows: Fixed Speed Wind Turbines (FSWTs) and Variable Speed Wind Turbines (VSWTs). There have been tremendous improvements in wind turbine technology over the years, from FSWTs to VSWTs, as a result of fast innovations and advanced developments in power electronics. Thus, the VSWTs have better wind energy capture and conversion efficiencies, less acoustic noise and mechanical stress, and better power quality in power grids without support from external reactive power compensators due to the stochastic nature of wind energy. The two most widely employed VSWTs in wind farm development are the Doubly Fed Induction Generator (DFIG) and the Permanent Magnet Synchronous Generator (PMSG) wind turbines. In order to solve transient stability intricacies during power grid faults, this book proposes different control strategies for the DFIG and PMSG wind turbines.




Use of Services for Family Planning and Infertility, United States, 1982


Book Description

The 1982 statistics on the use of family planning and infertility services presented in this report are preliminary results from Cycle III of the National Survey of Family Growth (NSFG), conducted by the National Center for Health Statistics. Data were collected through personal interviews with a multistage area probability sample of 7969 women aged 15-44. A detailed series of questions was asked to obtain relatively complete estimates of the extent and type of family planning services received. Statistics on family planning services are limited to women who were able to conceive 3 years before the interview date. Overall, 79% of currently mrried nonsterile women reported using some type of family planning service during the previous 3 years. There were no statistically significant differences between white (79%), black (75%) or Hispanic (77%) wives, or between the 2 income groups. The 1982 survey questions were more comprehensive than those of earlier cycles of the survey. The annual rate of visits for family planning services in 1982 was 1077 visits /1000 women. Teenagers had the highest annual visit rate (1581/1000) of any age group for all sources of family planning services combined. Visit rates declined sharply with age from 1447 at ages 15-24 to 479 at ages 35-44. Similar declines with age also were found in the visit rates for white and black women separately. Nevertheless, the annual visit rate for black women (1334/1000) was significantly higher than that for white women (1033). The highest overall visit rate was for black women 15-19 years of age (1867/1000). Nearly 2/3 of all family planning visits were to private medical sources. Teenagers of all races had higher family planning service visit rates to clinics than to private medical sources, as did black women age 15-24. White women age 20 and older had higher visit rates to private medical services than to clinics. Never married women had higher visit rates to clinics than currently or formerly married women. Data were also collected in 1982 on use of medical services for infertility by women who had difficulty in conceiving or carrying a pregnancy to term. About 1 million ever married women had 1 or more infertility visits in the 12 months before the interview. During the 3 years before interview, about 1.9 million women had infertility visits. For all ever married women, as well as for white and black women separately, infertility services were more likely to be secured from private medical sources than from clinics. The survey design, reliability of the estimates and the terms used are explained in the technical notes.