Today’s homes and various establishments continually become dependent on electric power. Different business operations run on electricity, as well as a variety of household appliances. With this, it has become more and more important for UPS systems to be more efficient and reliable. They need to be designed to suit the applications they have to serve. A UPS does two important things – it maintains a regulated, stable source of power when AC power supply is present and it provides a secure source of power when the mains supply is out.

There are three primary types of static UPS available today and they are the following: online, offline, and line interactive UPS systems (uninterrupted power supply systems). Usually, line interactive and offline UPS systems are found in homes and small offices. In contrast, online types are typically used by data centers, where they are utilized in bigger applications that ask for superior reliability and electrical performance. These three UPS types differ in their abilities to offer security and power protection and each of them is designed to work perfectly in their respective range of applications. To do this, their designs incorporate individual parts (inverters, rectifiers, batteries, filters, and bypasses) that must work in harmony.

From the mains power supply, alternating current is converted to direct current by means of an important electronic component – the rectifier. This rectifier is important in a UPS system because it charges the battery pack of the UPS, which serves as the back-up power source when the mains fail. The rectifier also supplies this DC current to the inverter. Rectifiers come in transformer-based or transformer-less designs that are sometimes packed with booster converters. The battery pack, meanwhile, may be consisted of a single battery string or multiples strings that are connected in parallel, where strings being comprised of one or more blocks of batteries in series.

Filters are also found in UPS systems because they protect them, as well as the connected loads, from electro-magnetic and radio frequency interference. EMI and RFI from such devices are always purposely kept in minimum since they induce noise and harmful electrical spikes. Suppressing peak input voltages to levels that are acceptable is a must in order to keep the efficiency of UPS systems in check.

Meanwhile, the inverter is another integral part of a UPS system because it is what creates the necessary AC power for the connected load. Its size limits the load capacity of the device, measured in volt-amps (VA). Inverters of offline and line interactive UPS are normally in standby and are only used when the mains power supply fails or fluctuates. Online UPS types, classified as VFI (voltage and frequency independent), in contrast, have inverters that are designed for continuous operation.

Online UPS systems have automatic bypasses too and are the reason why they perform well in what they do. In order to protect critical equipments, these bypasses provide a fail safe plan in case system failure occurs. On such events, the bypass by design transfers the connection of the load to an alternate power source so system operation continues without fail. When the system faults are checked, they also have the ability to go back online.