What are the main types of UPS?
UPSs come in three major varieties, which are also known as topologies:
Single-conversion systems
In normal operation, these feed incoming utility AC power to IT equipment. If the AC input supply falls out of predefined limits, the UPS utilizes its inverter to draw current from the battery, and also disconnects the AC input supply to prevent backfeed from the inverter to the utility.
The UPS stays on battery power until the AC input returns to normal tolerances or the battery runs out of power, whichever happens first. Two of the most popular single-conversion designs are standby and line-interactive:
- Standby UPSs allow IT equipment to run off utility power until the UPS detects a problem, at which point it switches to battery power. Some standby UPS designs incorporate transformers or other devices to provide limited power conditioning as well.
- Line-interactive UPSs regulate input utility voltage up or down as necessary before allowing it to pass through to protected equipment. However, like standby UPSs, they use their battery to guard against frequency abnormalities.
Double-conversion systems
As the name suggests, these devices convert power twice. First, an input rectifier converts AC power into DC and feeds it to an output inverter. The output inverter then processes the power back to AC before sending it on to IT equipment.
This double-conversion process isolates critical loads from raw utility power completely, ensuring that IT equipment receives only clean, reliable electricity.
In normal operation, a double-conversion UPS continually processes power twice. If the AC input supply falls out of predefined limits, however, the input rectifier shuts off and the output inverter begins drawing power from the battery instead.
The UPS continues to utilize battery power until the AC input returns to normal tolerances or the battery runs out of power, whichever occurs sooner. In case of a severe overload of the inverter, or a failure of the rectifier or inverter, the static switch bypass path is turned on quickly, to support the output loads.
Multi-mode systems
These combine features of both single and double conversion systems while providing substantial improvements in both efficiency and reliability:
• Under normal conditions, the system operates in line-interactive mode, saving energy and money while also keeping voltage within safe tolerances and resolving common anomalies found in utility power.
• If AC input power falls outside of preset tolerances for line-interactive mode, the system automatically switches to double-conversion mode, completely isolating IT equipment from the
incoming AC source.
• If AC input power falls outside the tolerances of the double-conversion rectifier, or goes out altogether, the UPS uses the battery to keep supported loads up and running. When the generator comes online, the UPS switches to double-conversion mode until input power stabilizes.
Then it transitions back to high-efficiency line-interactive mode. Multi-mode UPSs are designed to dynamically strike an ideal balance between efficiency and protection.
Under normal conditions, they provide maximum efficiency. When problems occur, however, they automatically sacrifice some efficiency to deliver maximum levels of protection. The end result is that data centers can save tens of thousands a year on energy without compromising data center performance or reliability.
