voltage and frequency independent (UPS) (VFI)

The VFI (Voltage and Frequency Independent) classification used in UPS protection class 1 states that UPS systems are relatively insensitive to changes in frequency or voltage.

The online concept of an uninterruptible power supply (UPS).

The VFI classification represents UPS systems that are online, double- conversion for continuous operation. VFI devices completely disconnect the secondary from the mains voltage and supply the connected systems exclusively from the accumulators via an inverter. There is no direct connection between the primary mains supply and the secondary voltage, apart from a possible bypass operation in case of overload.