The central design of an uninterruptible power system (UPS) is categorized as its topology. Of the three primary UPS technologies available today — standby, line-interactive and online — each offers different performance characteristics and varying degrees of protection. It’s important to recognize that not all UPSs are not created equal.
Determining the best topology for your facility depends on a number of factors, including the level of reliability and availability required, as well as the type of equipment being protected and the overall application/environment. Various UPS topologies are appropriate for different uses, but no single UPS type is ideal for all applications. Consider the following:
Standby — Also referred to as an off-line or passive system, standby topology provides the most basic type of UPS protection. Safeguarding connected equipment against three of the nine most common power problem — power failures, sags and surges — the standby UPS allows equipment to run off of utility power until it detects a problem. At that point, the UPS switches to the battery. Standby UPSs are best suited for less critical applications such as office environments, provided that the power supply is not subject to frequent disruptions. While an attractive alternative from a cost perspective, the downside to standby UPSs is that they do not buffer equipment against other power anomalies, and they must resort to batteries frequently, which can reduce battery runtime and service life.
Line-interactive — A UPS with line-interactive topology is designed to shield connected devices from power failures, sags and surges like a standby model does, but it also provides protection against under- and over- voltage conditions. Typically used to safeguard enterprise network and IT applications, the line-interactive UPS is controlled by a microprocessor that monitors the quality of incoming power and reacts to fluctuations. One of the biggest advantages of the line-interactive topology is that it compensates for undervoltage and overvoltage circumstances without using the batteries. These systems provide more protection than standby UPSs, with better power conditioning and regulation that helps prolong battery life. Battery usage is lower than a standby UPS, but still higher than an online model.
Online — An online or double-conversion UPS is designed to deliver continuous protection against all nine of the most common power problems. Supplying a consistent power quality regardless of any incoming instabilities, the output voltage of an online UPS is entirely regenerated by a sequence of AC to DC conversion, followed by DC to AC conversion in order to create power supply without any electrical interference. During erratic power or fleeting disturbances when AC input power falls outside of preset tolerances for line-interactive mode, the online UPS switches to online double-conversion mode, completely isolating equipment from incoming power. If power is lost altogether, or the input power exceeds the tolerances of the rectifier, the UPS will rely on the battery to keep loads operating, then convert back to high-efficiency mode when it is safe. Online UPSs are the best choice for critical applications or those involving highly sensitive equipment, such as data centers, communications hubs and other mission-critical installations where continuous, clean power is a business-critical requirement.
While all three UPS topologies outlined above meet the input voltage requirements for IT equipment, there are significant differences in both performance and demands on the battery. If you need assistance determining the optimal topology for your environment, Unified Power can help you to properly identify and compare systems.