Specifications

15
Types of Uninterruptible Power Supply
(UPS)
Line Interactive
Uninterruptible
Power Supply (VI)
On this type of UPS the inverter is
connected in parallel to the AC input
and also charges the battery (interactive
operation in reversible mode).
When the AC input supply is not within
strict amplitude and frequency
tolerances, the load is powered by the
inverter through the battery.
The normal inverter output waveform is
a stepwave or squarewave.
This technique is rarely used for high
power ratings as frequency regulation is
not possible. Active Standby (or Line
Interactive) technology is a recent
development made possible by the
advent of microprocessors. The UPS is
fully controlled by a microprocessor
which monitors the quality of the mains
power supply and reacts to any
variations. In the event of a power
problem, the UPS transfers the load to
the batteries to supply stabilised power.
It is increasingly frequent to add a
voltage compensation circuit, called a
“booster”, that is enabled in the event of
prolonged voltage drops.
Passive Standby
Uninterruptible
Power Supply
(Off-line) (VFD)
This type of UPS, also called Off-line
UPS, is connected in parallel to the
normal AC source. The current is filtered
in order to attenuate the most frequent
forms of disturbance. In the event of a
power problem the UPS transfers the
load to the batteries to supply stabilised
power: the inverter only switches on
when the mains fails or fluctuates
outside the input voltage tolerances of
the EMI filter or if it is fitted with
Automatic Voltage Stabiliser (AVS).
Bypass
A.C. input
Static switch
A.C. output
A.C. input
Automatic Voltage Regulator
Inverter
normal mode
battery mode by pass mode
Battery
AVR
Bypass
A.C. input
Static switch
A.C. output
Battery
A.C. input
Battery charger
Inverter
normal mode battery mode