Three phase parallel processing UPS using multi-functional inverter

A parallel processing uninterruptible power supply (UPS) system is proposed in which a three-phase pulse-width modulation (PWM) inverter is connected in parallel to a utility power source through an inductance and an electronic switch. In this system, when the utility power is on, the inverter controls the voltage regulation of the inductance so as to control the output voltage constantly in synchronization with the utility. The batteries are charged by the inverter at the same time. The inverter also absorbs the load harmonics so as to obtain a sinusoidal output voltage. When a power failure happens, the electronic switch in the input line is turned off and the inverter operates alone with no break of power supply to the load. Using only one inverter, the parallel processing UPS realizes a combined system of a constant voltage power source, an uninterruptible power supply, and a harmonics absorbing active filter. This system can also link new types of DC power sources, such as fuel cells or photovoltaic cells, to utility power systems.<>