Types of UPS systems

Uninterruptible power supply or UPS system enables you to save data and shut down the computer gracefully, when there is sudden power failure. It enables you to automate backup and shut down procedures if there is power failure while you are away from the computer.

There are different types of UPS systems available. The different types of UPS have different features that make them more or less suitable for different applications. There is no single UPS type that is applicable for all applications.It is widely believed that standby UPS and online UPS are the only two major types of UPS systems. The most common types of UPS systems are Standby UPS, Line Interactive UPS, Standby on-line hybrid UPS, Standby-Ferro UPS, True On-line UPS, Double Conversion On-Line UPS, Delta Conversion On-Line UPS. Generally, the on-line UPS is much more expensive than Standby UPS.

The Standby UPS is the most common type of UPS system used for Personal Computers. It monitors the power line and switches to battery power as soon as it detects a problem. Standby UPS is simple, least expensive, highly efficient, and small in size. A Standby UPS is not that much suitable to deal with voltage sags and low frequency conditions, and may damage your sensitive digital equipment. The system causes unavoidable momentary loss of power which is generally not good for modern computing and telecommunications equipment. The Standby UPS systems can provide adequate noise filtration and surge suppression with the use of proper filter and surge circuitry.

The Line Interactive UPS system is the one used for small business, Web, and departmental servers. It uses a continuously on-line battery with an inverter/converter to keep the battery connected to the output. It provides instant back-up, and deals slightly with voltage and frequency problems. Line Interactive UPS system is very efficient, highly reliable, and low cost and provides superior power protection.

UPS under 10kVA use the Standby On-Line Hybrid topology. In this type of UPS, the inverter circuit is operated in the on-line mode and the dc-dc converter circuit is operated in the standby mode.

The Standby-Ferro UPS was once the dominant form of UPS in the 3-15kVA range. Standby-Ferro UPS has high reliability, excellent line filtering, very low efficiency, and instable when used with some generators and computers.

An on-line UPS system avoids the momentary power lapses by constantly providing power from its own inverter, even if the power line is functioning properly. True On-line UPS handles all voltage and frequency problems since all AC input is converted to DC and then back to AC at the proper voltage and frequency. It provides instant back-up since the battery is always in the circuit.

The Double Conversion On-Line UPS is the most common type of UPS above 10kVA. This UPS has reduced reliability over other designs, causes reduced efficiency and increased heat generation.

The Delta Conversion On-Line UPS eliminates the drawbacks of the Double Conversion On-Line design and is available in the range of 5kVA to 1 MW. During steady state conditions the Delta Converter allows the UPS to deliver power to the load with much greater efficiency than the Double Conversion design.

Still there is much confusion in the marketplace about the different types of UPS systems and their characteristics. A wise decision has to be made to choose the appropriate UPS for an application, based on the characteristics, advantages and disadvantages of the UPS.