UPS (Uninterruptible power supply)
An Uninterruptible Power Supply also known as no break-system is a device which maintains a continuous supply of electric power to computers and other equipment for a limited period of time in the event of a power interruption.
A UPS usually has a battery and an electronic switch which can convert the battery current into power. Some types of UPS also have a detection switch which monitors whether power is still being supplied and switches over to emergency power as soon as the supply is interrupted. Typical characteristics of a UPS are the maximum capacity to be delivered and the maximum time during which this power can be delivered. Smaller UPS units can deliver e.g. 500 VA and feed a PC during several tens of minutes. Large UPS systems can supply up to several MVA (MegaVA) and provide entire computer floors with power, usually until a (diesel) generator has been started up.
Most UPS units are also equipped with an interface to the PC, so that the UPS can switch off the PC if the battery power supply drops to a certain lower limit. The outstanding advantage of a UPS is that power supply is maintained without any interruption. This is the reason why this system is applied in e.g. hospitals.
UPS designs
A UPS can be designed in various ways. The most reliable method is the double conversion method: The power supply (alternating current) is always converted into direct current. This direct current is used to charge the batteries. Next the direct current in the batteries is converted back to alternating current. So the PC is always powered by the batteries that are being constantly recharged. Thanks to the electronic regulator, the new alternating current is always at the right voltage and frequency. Such a UPS thus also resolves problems other than power failures, such as short power dips, peaks, grid contamination etc. As a double conversion UPS is always in operation, it provides optimal reliability.
The big disadvantage of a double conversion UPS is that the power needs to be converted twice, which impairs the efficiency. However, thanks to modern technologies, professional UPS units can now offer up to 95% efficiency.
Alternative designs are the off-line UPS, which switches on very rapidly (within 2 ms) in the event of a power failure and the line-interactive UPS. The latter exists in different versions which all have in common that the feeding power flow is "improved" by a buck and boost transformer which brings higher and lower voltages down or up to the required nominal value before it goes to the connected equipment; but when the power falls away the UPS must switch over to be able to supply all the power. The disadvantage of all these methods is that there is no certainty that the UPS actually works until a power disruption occurs.
One extremely important component of the UPS is the battery. The greater the battery capacity, the greater the autonomy time, i.e. the time that the UPS can continue to feed the equipment autonomously without power supply.
UPS applications
The SOHO market (Small office / Home office) is coming to the fore, also within the UPS world. This calls for small, compact UPS products in the form of e.g. a plug/junction box.
In addition, a lot of IT and Telecom equipment is placed in standardised 19 inch racks. UPS manufacturers are responding to this by delivering UPS products that fit in to these racks (Rackmount UPS) and are low enough in height to leave sufficient room for the IT and Telecom equipment being protected.
