12,039 research outputs found
Fuzzy Controller for Matrix Converter System to Improve its Quality of Output
In this paper, Fuzzy Logic controller is developed for ac/ac Matrix
Converter. Furthermore, Total Harmonic Distortion is reduced significantly.
Space Vector Algorithm is a method to improve power quality of the converter
output. But its quality is limited to 86.7%.We are introduced a Cross coupled
DQ axis controller to improve power quality. The Matrix Converter is an
attractive topology for High voltage transformation ratio. A Matlab / Simulink
simulation analysis of the Matrix Converter system is provided. The design and
implementation of fuzzy controlled Matrix Converter is described. This AC-AC
system is proposed as an effective replacement for the conventional AC-DC-AC
system which employs a two-step power conversion.Comment: 11 page
Information Flow Model for Commercial Security
Information flow in Discretionary Access Control (DAC) is a well-known difficult problem. This paper formalizes the fundamental concepts and establishes a theory of information flow security. A DAC system is information flow secure (IFS), if any data never flows into the hands of owner’s enemies (explicitly denial access list.
Theory of photospheric emission from relativistic outflows
In this paper we reexamine the optical depth of ultrarelativistic spherically
symmetric outflows and reevaluate the photospheric radius for each model during
both the acceleration and coasting phases. It is shown that for both the wind
and the shell models there are two asymptotic solutions for the optical depth
during the coasting phase of the outflow. In particular we show that quite
counterintuitively a geometrically thin shell may appear as a thick wind for
photons propagating inside it. For this reason we introduce notions of photon
thick and photon thin outflows, which appear more general and better physically
motivated with respect to winds and shells. Photosphere of relativistic outflow
is a dynamic surface. We study its geometry and find that the photosphere of
photon thin outflow has always a convex shape, while in the photon thick one it
is initially convex (there is always a photon thin layer in any outflow) and
then it becomes concave asymptotically approaching the photosphere of an
infinitely long wind. We find that both instantaneous and time integrated
observed spectra are very close to the thermal one for photon thick outflows,
in line with existing studies. It is our main finding that the photospheric
emission from the photon thin outflow produces non thermal time integrated
spectra, which may be described by the Band function well known in the GRB
literature. We find that energetic GRBs should produce photon thin outflows
with photospheric emission lasting less than one second for the total energy
erg and baryonic loading parameter . It means
that only time integrated spectra may be observed from such GRBs.Comment: Revision of the previous version, new effect is discussed.
Conclusions remain unchange
Back-to-back Converter Control of Grid-connected Wind Turbine to Mitigate Voltage Drop Caused by Faults
Power electronic converters enable wind turbines, operating at variable
speed, to generate electricity more efficiently. Among variable speed operating
turbine generators, permanent magnetic synchronous generator (PMSG) has got
more attentions due to low cost and maintenance requirements. In addition, the
converter in a wind turbine with PMSG decouples the turbine from the power
grid, which favors them for grid codes. In this paper, the performance of
back-to-back (B2B) converter control of a wind turbine system with PMSG is
investigated on a faulty grid. The switching strategy of the grid side
converter is designed to improve voltage drop caused by the fault in the grid
while the maximum available active power of wind turbine system is injected to
the grid and the DC link voltage in the converter is regulated. The methodology
of the converter control is elaborated in details and its performance on a
sample faulty grid is assessed through simulation
The lowest modes around Gaussian solutions of tensor models and the general relativity
In the previous paper, the number distribution of the low-lying spectra
around Gaussian solutions representing various dimensional fuzzy tori of a
tensor model was numerically shown to be in accordance with the general
relativity on tori. In this paper, I perform more detailed numerical analysis
of the properties of the modes for two-dimensional fuzzy tori, and obtain
conclusive evidences for the agreement. Under a proposed correspondence between
the rank-three tensor in tensor models and the metric tensor in the general
relativity, conclusive agreement is obtained between the profiles of the
low-lying modes in a tensor model and the metric modes transverse to the
general coordinate transformation. Moreover, the low-lying modes are shown to
be well on a massless trajectory with quartic momentum dependence in the tensor
model. This is in agreement with that the lowest momentum dependence of metric
fluctuations in the general relativity will come from the R^2-term, since the
R-term is topological in two dimensions. These evidences support the idea that
the low-lying low-momentum dynamics around the Gaussian solutions of tensor
models is described by the general relativity. I also propose a renormalization
procedure for tensor models. A classical application of the procedure makes the
patterns of the low-lying spectra drastically clearer, and suggests also the
existence of massive trajectories.Comment: 31 pages, 8 figures, Added references, minor corrections, a
misleading figure replace
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