UPS = Uninterruptible power supply. Usually the backup power switch within 10ms. Can be used as a backup power source for a computer for a short period of time, in case of power fluctuation
IPS = Instant Power Supply. Switching time is large and can be 1s. Used as backup power. Has large capacity.
AVR = Automatic Voltage Regulator, Automatically controls an Input voltage, to minimize fluctuation.
Both the IPS and UPS type systems employ Direct Current (DC) to Alternating Current (AC) inverters to provide AC power of proper frequency and voltage and also a charging system to maintain internal DC batteries at full charge. IPS and UPS operation is primarily distinguished in the operation of the inverter. For the IPS, the inverter is ON only during a power outage and is solely powered by internal batteries. For the UPS, the inverter is always ON powering the load. The inverter is normally powered from the AC line and, during a power outage, powered from the internal batteries.
The above mentioned may deploy the usage of an AVR for their voltage regulation needs.