Patent ID: 7141892

Claim:
A power supply method of a line interactive uninterruptible power supply (UPS) comprising the steps of: providing a first switching unit to be coupled between a line voltage and a bi-directional AC/AC converter, wherein the first switching unit has a first input terminal and a second input terminal respectively coupled to the line voltage; and two output terminals; providing a switching means to be couple to the first switching unit, the bi-directional AC/AC converter and a load, wherein the load has two ends; determining an operating mode of the line interactive UPS from a by-pass mode, a line voltage conversion mode and a battery mode, based on the stability of a line voltage coupled to the UPS; wherein in the by-pass mode, the line voltage is directly coupled to the load when the line voltage is stable; wherein in the line voltage conversion mode, the line voltage is further compared with a predetermined normal voltage, if the line voltage is higher than the normal voltage, a compensation voltage with a phase that is opposite to that of the line voltage is coupled to the line voltage in series; wherein if the line voltage is lower than the normal voltage, a compensation voltage with a phase that is the same as that of the line voltage is coupled to the line voltage in series, wherein the compensation voltage is generated by the bi-directional AC/AC power converter; wherein in the battery mode, a DC power supply unit of the line interactive UPS provides the load with power.