136,497 research outputs found
Small-Signal Modelling and Analysis of Doubly-Fed Induction Generators in Wind Power Applications
The worldwide demand for more diverse and greener energy supply has had a significant
impact on the development of wind energy in the last decades. From 2 GW in 1990,
the global installed capacity has now reached about 100 GW and is estimated to grow to
1000 GW by 2025. As wind power penetration increases, it is important to investigate its
effect on the power system. Among the various technologies available for wind energy
conversion, the doubly-fed induction generator (DFIG) is one of the preferred solutions
because it offers the advantages of reduced mechanical stress and optimised power capture
thanks to variable speed operation. This work presents the small-signal modelling and
analysis of the DFIG for power system stability studies.
This thesis starts by reviewing the mathematical models of wind turbines with DFIG
convenient for power system studies. Different approaches proposed in the literature for
the modelling of the turbine, drive-train, generator, rotor converter and external power
system are discussed. It is shown that the flexibility of the drive train should be represented
by a two-mass model in the presence of a gearbox.
In the analysis part, the steady-state behaviour of the DFIG is examined. Comparison
is made with the conventional synchronous generators (SG) and squirrel-cage induction
generators to highlight the differences between the machines. The initialisation of the
DFIG dynamic variables and other operating quantities is then discussed. Various methods
are briefly reviewed and a step-by-step procedure is suggested to avoid the iterative
computations in initial condition mentioned in the literature.
The dynamical behaviour of the DFIG is studied with eigenvalue analysis. Modal
analysis is performed for both open-loop and closed-loop situations. The effect of parameters
and operating point variations on small signal stability is observed. For the
open-loop DFIG, conditions on machine parameters are obtained to ensure stability of
the system. For the closed-loop DFIG, it is shown that the generator electrical transients
may be neglected once the converter controls are properly tuned. A tuning procedure is
proposed and conditions on proportional gains are obtained for stable electrical dynamics. Finally, small-signal analysis of a multi-machine system with both SG and DFIG is
performed. It is shown that there is no common mode to the two types of generators.
The result confirms that the DFIG does not introduce negative damping to the system,
however it is also shown that the overall effect of the DFIG on the power system stability
depends on several structural factors and a general statement as to whether it improves or
detriorates the oscillatory stability of a system can not be made
Teaching Competency of Teacher of Building Drawing Skill In SMK N 1 Sedayu Bantul
Teacher is an important element for the improvement of Indonesia’s
education because teacher has a role to delivery subject matter directly to the
student. The teacher must have good teaching competency so the aim of learning
can be achieved. This research is explain how teaching competency in productive
subject matter, building drawing course in SMK N 1 Sedayu Bantul.
In this research the writer take research object was 6 teachers of building
drawing course in SMK N 1 Sedayu Bantu. Data collection technique was indirect
observation in 3 kinds of questionnaire. First questionnaire was for student
participant, the second was for head master participant. The questionnaire
consisted of 4 answer choice, (BS) very good, (B) good,(K) minus,(KS) very
minus. The third was portfolio questionnaire for teacher participant. Data of this
research was analyzed with descriptive statistics technique and descriptive
quantitative.
Result of the research show that in general teaching competency teacher in
productive subject matter, building drawing course SMK N 1 Sedayu Bantul can
be categorized in good category. From 6 indicators of teaching competency 83,3%
were good and 16,66% was minus. The indicators categorized as good category
were indicator of teaching instrument usage, giving motivation, indicator of
assessment, the use of teaching method, interaction between teacher and student,
However, for presentation matter was categorized as minus. Second, result of this
research indicated that there was correlation between head master assessment and
student assessment for teaching competency. The student assessment was more
objective than head master’s assessment because the number of student was
bigger than the number of head masters that just one person. The student had
enough time to fill up the questionnaire so the result was more accurate. The
student was more understand because the teacher aught them every day. Third,
this research indicated that there was no correlation between assessment of teacher
portfolio and their teaching competency, it means, for the student, high result of
portfolio assessment didn’t increase the teachers’ teaching competency. So,
portfolio assessment can’t be absolute reference to assess the teacher competency.
Keyword: Teaching competency, Productive subject matter, Pedagogic
competency, Personal competenc
Intermediary's Elicitation and Patron's Retrieval Satisfaction
[[abstract]]An elicitation is a verbal request for information reflecting one's interests, concerns or perplexities in conversation. Elicitation behavior in studies of information retrieval interaction is, in fact, the micro-level of information-seeking behavior in which the user and the intermediary exchange information to fill the gaps in one's internal state of knowledge. This study aims to understand the intermediary's elicitation behavior in terms of linguistic forms, communicative functions (illocutionary force) and utterance purposes (semantic contents) and further to identify the relationship between intermediary's individual differences and search results satisfaction. Research methods include participatory observation, conversation analysis, content analysis and statistical analysis of elicitation frequencies and questionnaires. Our research results successfully identify the three dimensions of intermediary's elicitation behavior and characterize intermediary's inquiring minds and elicitation styles. Further analysis shows that there exists a significant relationship between inquiring minds/elicitation styles and user's relevance judgment of search results.
An Extrapolation of Operator Valued Dyadic Paraproducts
We consider the dyadic paraproducts \pi_\f on \T associated with an
\M-valued function \f. Here \T is the unit circle and \M is a tracial
von Neumann algebra. We prove that their boundedness on L^p(\T,L^p(\M)) for
some implies their boundedness on L^p(\T,L^p(\M)) for all
provided \f is in an operator-valued BMO space. We also consider
a modified version of dyadic paraproducts and their boundedness on
$L^p(\T,L^p(\M))
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