Online term refers to the condition when converter is in operation when power in the line is present. Offline mode refers to a condition when converter operation start after the main line is off or not available. Therefore, online UPS is a stage which is introduced between the load and mains.
Types of UPS. Generally, the UPS system is categorised into On-line UPS, Off- lineUPS and Line interactive UPS. Other designs include Standby on-line hybrid, Standby-Ferro, Delta conversion On-Line
The key difference between Online UPS and Offline UPS lies in their working. AnOnline UPS supplies the AC power through a rectifier and inverter circuit even when the AC mains power is available. On the contrary, the offline ups directly supply the AC mains power to the load circuit when the power supply is available.