Patent ID: 6445089
Filing Date: 2002-09-03
Classification: H02J

Abstract:
An uninterruptible power system comprising:an abnormal voltage detection circuit for detecting voltage reduction abnormality of a commercial power supply; an AC switch turned on to permit AC power to be fed from said commercial power supply to a load when said commercial power supply is in a normal condition and turned off when said commercial power supply falls into an abnormal condition; a storage battery; a power converter of the voltage control type arranged between said AC switch and said storage battery; said power converter carrying out power rectifying operation of converting AC power of said commercial power supply into DC power to charge said storage battery by said DC power and active filter operation of flowing a current for compensating a harmonic current and/or a reactive current flowing to said load when said commercial power supply is in the normal condition; said power converter carrying out power inverting operation of inverting DC power into AC power to feed the AC power to said load mainly using said storage battery as a power supply therefor when said commercial power supply is in a condition other than said silent condition; a control command generation means for outputting a control command to said power converter for feeding AC power to said load without a power failure; said control command generation means including a voltage control system for outputting a voltage control command which permits said power converter to carry out said power inverting operation and a current control system for outputting a current control command which permits said power converter to carry out said power rectifying operation and active filter operation; and a reference voltage generating circuit for generating a reference sinusoidal voltage synchronized with said commercial power supply; said current control system being constructed so as to provide an input current command value on the basis of a multiplied value obtained by multiplication between a differential voltage between a DC command voltage commanded by a DC voltage command and a DC-side voltage of said power converter and an output of said reference voltage generating circuit, and to thereby output said current control command on the basis of a value obtained by subtracting a load current value from said input current command value; said current control system being constructed so as to use an AC current flowing through said AC switch or a value corresponding to said AC current as said input current command value when said abnormal voltage detection circuit carries out detection of said voltage reduction abnormality.