Industrial UPSs are regarded as fully customized power supply systems for rugged environments and designed particularly to safeguard critical loads in industrial applications where voltage transients, created by degraded mains supply, can seriously damage both UPS and the critical load.  Industrial UPS Systems are fully flexible and customizable and designed for active–on line installation between the power source, by-pass source and critical load where the inverter delivers regulated AC voltage and frequency to the load and rectifier delivers regulated DC voltage / current to the DC load at all times with- out interruption.
The power conversion process isolates the critical load from the normal mains disturbances and iso- lates the mains from load induced reflected harmon- ics affecting other loads connected to the input mains feeder. The rectifier converts AC power into DC to charge maintenance free lead acid or nickel cadmium batteries; it also provides the necessary DC for continuously rated capacity of the inverter. IGBT semiconductor modules are used in PWM inverter and the control logic creates the precise sinusoidal output waveform with a very low harmonic content. Thyristor semiconductor modules are also used in rectifier for reliable operation.
The system consists of rectifier / charger, inverter, static bypass, maintenance bypass, rectifier isola- tion transformer,  inverter  isolation  transformer, bypass  line  isolation  transformer,  automatic  line stabilizer, DC  distribution,  AC  distribution,  con- trols  and  monitoring.  The  AC  output  of  the  in- verter is connected to the critical load, the stor- age  battery  is  connected  between  the  inverter input  and  rectifier / charger output  through  a battery isolation MCB. The normal AC input pow- er is connected to the rectifier; the bypass circuit also takes power from the same power source to provide power for the critical load during bypass operation  when  the  system  is  in  maintenance mode.