101,860 research outputs found
Sampled-Data and Harmonic Balance Analyses of Average Current-Mode Controlled Buck Converter
Dynamics and stability of average current-mode control of buck converters are
analyzed by sampled-data and harmonic balance analyses. An exact sampled-data
model is derived. A new continuous-time model "lifted" from the sampled-data
model is also derived, and has frequency response matched with experimental
data reported previously. Orbital stability is studied and it is found
unrelated to the ripple size of the current-loop compensator output. An
unstable window of the current-loop compensator pole is found by simulations,
and it can be accurately predicted by sampled-data and harmonic balance
analyses. A new S plot accurately predicting the subharmonic oscillation is
proposed. The S plot assists pole assignment and shows the required ramp slope
to avoid instability.Comment: Submitted to International Journal of Circuit Theory and Applications
on August 9, 2011; Manuscript ID: CTA-11-016
Long zero-free sequences in finite cyclic groups
A sequence in an additively written abelian group is called zero-free if each
of its nonempty subsequences has sum different from the zero element of the
group. The article determines the structure of the zero-free sequences with
lengths greater than in the additive group \Zn/ of integers modulo .
The main result states that for each zero-free sequence of
length in \Zn/ there is an integer coprime to such that if
denotes the least positive integer in the congruence class
(modulo ), then . The answers to a number of
frequently asked zero-sum questions for cyclic groups follow as immediate
consequences. Among other applications, best possible lower bounds are
established for the maximum multiplicity of a term in a zero-free sequence with
length greater than , as well as for the maximum multiplicity of a
generator. The approach is combinatorial and does not appeal to previously
known nontrivial facts.Comment: 13 page
Dynamics of D3-D7 Brane Inflation in Throats
Dynamics of D3-branes in models of warped D3-D7 inflationary set up is
studied where perturbative correction to the K\"ahler potential and
the nonperturbative corrections to the superpotential are included. It is shown
that a dS minimum can be obtained without introducing anti-branes. Some
specific configurations of D7-branes embedding were studied. After stabilizing
the angular directions, it is shown that the resulting D3-D7 potential of the
radial position of the D3-brane is too steep to allow slow-roll inflation.
Depending on D7-branes embedding and the stabilized angular directions, the
mobile D3-brane can move either towards the tip of the throat or towards the
D7-branes.Comment: minor changes, to appear in JHE
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