Power Electronics Electrônica de Potência Página do Eng. Armando Cavero Miranda

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sábado, 5 de março de 2011

A Novel Control Strategy for Parallel Operation of Three-phase UPS Inverters

A Novel Control Strategy for Parallel Operation of
Three-phase UPS Inverters

By Sang-Hoon Lee
Under the supervision of Prof. Dong-Seok Hyun, Ph.D.
Dept. of Electrical Engineering
The Graduate School of Hanyang University

Parallel operation of uninterruptible power supply (UPS) system has been used to
increase power capacity of the system or to secure reliable supply of power to critical loads.
During parallel operation, load sharing control to maintain the current balance is critical
for reliable operation, since load sharing is very sensitive to differences in components of
each module such as amplitude /phase difference, line impedance, and output LC filters. To
solve these problems various control algorithms have been researched. However, these
methods cannot be applied to UPS systems with different ratings. For this case, master and
slave control algorithms for parallel operation is adequate. If the ratings of UPS systems are
different, the value of passive LC filters will be different, and it will affect current sharing.
This paper presents the general problems associated with parallel operation of UPS systems,
and control strategy for parallel operation with different ratings. The validity of the proposed
control strategy is investigated through simulation and experiment with two UPS systems.
FULL PAPER HERE:http://www.4shared.com/document/_SB8U20J/UPSPARALELO2.html

Characteristic Analyses of Commercial Single-phase High-efficiency Transformers

Characteristic Analyses of Commercial Single-phase High-efficiency Transformers
Abstract 　　The aim of this thesis is to analyze the influence of different lamination shape and its improvement on magnetic field distribution inside the iron core of single-phase transformers.
　　Traditionally, the laminated core is generally adopted and the laminated iron sheets are cut in E-shape and I-shape sheets to reduce core loss in the studied transformer. The reluctance of the magnetic flux path inside the iron core of the studied transformer is affected by the condition of press, shape of laminated core property, effective length and area of flux path. To reduce the reluctance between connection points, the E-shape and I-shape laminated sheets are interchanged to avoid obvious connection line between laminated sheets. This thesis is to simulate magnetic filed distribution of single-phase transformers using electromagnetic field software. The effectiveness of the improved E- and I-shape laminated core will be evaluated in depth for future design of single-phase low-voltage distribution transformers with high-quality, high efficiency, and low core loss.
　　For simulate the inrush current, another model of single-phase transformer written by FORTRAN is compared with experience in this thesis.

FULL THESIS HERE;http://etdncku.lib.ncku.edu.tw/ETD-db/ETD-search/getfile?URN=etd-0706104-111050&filename=etd-0706104-111050.pdf