Design And Development Of An Online UPS

Abstract

UPS (Uninterruptible Power System) protects different types of sensitive electrical equipment: computers, workstations, sales terminals, critical instrumentation, telecommunications systems, process control systems, etc. The UPS protects them from problems associated with utility power of poor quality, or a complete loss of power. Sensitive electrical equipment needs protection from electrical interference. Interference from outside the facility (such as lightning, power company accidents and radio transmissions) and interference from inside the facility (from motors, air conditioners, vending machines and arc welders, for example) can create problems in the AC power line to the sensitive equipment. The problems can be: power outage, low or high voltage, slow voltage fluctuation, frequency variations, differential and common-mode noise, transients, etc. There are mainly two types of UPS, first one is Off line UPS and second one is On line UPS. Based on topology used in converter and inverter, they are further classified in to full bridge and half bridge. Each of this topology has its own advantage and disadvantages. I am working on half bridge converter half bridge inverter topology based UPS. In half bridge converter and a half bridge inverter topology there are total four switches. A half-bridge converter is for AC/DC conversion section and a half-bridge inverter is for the DC/AC conversion section of an uninterruptible power system (UPS). In this topology based UPS it is possible to omit the isolating transformer because of common line between input and output. Also the UPS based on this topology are more efficient and smaller. But as using such a circuit required storage batteries of very high voltage, it is in particular not suitable as a type of circuit for small-capacity UPSs of the 1 to 3 kVA class. To solve out this problem we therefore conceived one technique in order to lower necessary storage battery voltage: that uses a bi-directional chopper. We incorporated this technique into a 1 kVA UPS respectively, allowing us to develop small, high -performance UPSs. The working of this bidirectional chopper is as below. When the mains is available the output of the half bridge converter is go for the input of half bridge inverter and at the same time it is step down using step Down chopper to battery voltage to charge the battery. And when the mains is not available the battery voltage is step up using step up chopper and give input to the half bridge inverter.