* Main author：Dept. of Railway Electrical and
Signaling Engineering, Seoul National
University of Science and Technology,
Candidate of MS
** Corresponding author：Dept. of Electrical and
Information Engineering, Seoul National
University of Science and Technology,
Professor
Tel：02-970-6415, Fax：02-978-2754
E-mail：joongho@seoultech.ac.kr
Abstract
A new droop control method which can be applied to 3-phase 4-wire uninterruptible power supply is
proposed in this paper. The droop control method for parallel operation is very attractive one as UPS
parallel operation can be carried out without any data communication devices provided among UPS
systems connected, but it reportedly shows a PnP(plug-and-play) problem. A basic reason why a
circulating current could flow among parallel-connected UPS systems is clearly investigated as well
when droop-controlled-ups systems are operated in the manner of PnP. The proposed algorithm is
deduced from the investigated result and is basically structured to keep a balanced frequency and
balanced voltage profile against power variation. This paper shows that balanced parallel operation of
droop control method can be obtained under unbalanced load as well as balanced load conditions .when PnP operation is needed and load change occurs.
LINK
http://www.koreascience.or.kr/article/ArticleFullRecord.jsp?cn=JMJGCE_2013_v27n4_88
https://www.mediafire.com/?gyedgrq3fd38alx
