There are three main types of UPS: off-line, on-line and line-interactive. The off-line is the most common type of UPS and can be found in homes and small businesses. Line-interactive UPSs are also popular with home users and small businesses, but are more slightly advanced than the off-line UPS. The on-line type is the most advanced type of UPS and is used in organizations where there is critical computing, and protecting the operation from power disturbances is extremely important.
A Standby UPS, also referred to as an off-line UPS, is used to protect a user computer and or other basic applications since it provides only partial power protection. It consists of a battery and a switch that senses irregularity in power supply. The computer uses power from the main source, but the UPS starts providing power when the main source is disconnected. In case of a power surge, the UPS passes the surge to another unit within it, until it reaches an acceptable level.
The Line-interactive UPS is more advanced than the off-line UPS, but less advanced than the on-line type. It can manage a lot of variations in input voltage, without resorting to the battery for power. It responds faster to a power failure than the stand-by UPS. You can use it at home and in business. Another variant of the line-interactive UPS is the Ferroresonant UPS.
A Line-interactive UPS is almost similar to the Standby UPS, but the difference is the source of power which comes from the UPS's battery, and not from the main source. It is also called a double-conversion or double-conversion online UPS. During normal operation, the on-line UPS is powered by the battery using the inverter, while the main source of power charges the battery. Its variations are double conversion and delta conversion UPS.