At times, power from a wall socket is neither clean nor uninterruptible. Many abnormalities such as blackouts, brownouts, spikes, surges, and noise can occur. Under the best conditions, power interruptions can be an inconvenience. At their worst, they can cause loss of data in computer systems or damage to electronic equipment. It is the function of an Uninterruptible Power Supply (UPS) to act as a buffer and provide clean, reliable power to vulnerable electronic equipment.
The basic concept of a UPS is to store energy during normal operation (through battery charging) and release energy (through DC to AC conversion) during a power failure.UPS systems are traditionally designed using analog components. Today these systems can integrate a microcontroller with AC sine wave generation, offering the many benefits listed below. [...]

Source: http://www.microchip.com