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PowerSure PSA Guide Specification
350 – 1000VA SL-23271 8/03
6
2.2.2 Bi-Directional Converter
2.2.2.1 General
The Bi-Directional Converter incorporates solid-state devices and control circuitry to
convert AC power to regulated DC power for battery charging; and convert DC power
from the battery to regulated and conditioned stepped-sinewave AC power for supporting
the critical load. The Bi-Directional Converter is a pulse width modulated (PWM)
design. The Bi-Directional Converter operates in the following modes:
1. In Normal mode of operation, the Bi-Directional Converter maintains the
battery system at a float charge.
2. In Battery mode of operation, the Bi-Directional Converter converts DC power
from the battery to regulated and conditioned stepped-sinewave AC power for
supporting the critical load.
3. In the recharge mode of operation, the Bi-Directional Converter converts AC
power to regulated DC power to recharge the battery.
2.2.2.2 Battery Recharge
The UPS contains a battery recharge rate designed to prolong battery life. The battery is
constant voltage charged to recharge and maintain the battery in a fully charged state.
Recharge time is 6 hours maximum to 90% rated capacity after discharge into full
resistive load.
2.2.2.3 Bi-Directional Converter DC Protection
The following DC shutdown levels protect the UPS:
DC Overvoltage Shutdown
DC Undervoltage Shutdown (End of Discharge)
DC Undervoltage Warning (Low Battery Reserve)
2.2.2.4 Output Protection
For output faults including short circuits and overloads, the UPS is protected by the input
circuit protector during Normal mode and by electronic current limiting during Battery
mode
.
2.2.2.5 Overload
The UPS is capable of supplying power for overloads exceeding 100% and up to 110%
of full load rating, continuously. A visual indicator and audible alarm indicate overload
operation. For greater current demands, the UPS employs circuit protector and electronic
current-limiting protection to prevent damage to components. The UPS is self-protecting
against any magnitude of connected output overload. The UPS control logic senses and
disconnects the UPS from the critical AC load and clears the protective circuit breaker
during Normal mode.
2.2.2.6 Output Frequency
An oscillator controls the output frequency of the UPS. The oscillator maintains the
output frequency to + 0.5 Hz of nominal when not synchronized to the utility/mains
source.
2.2.2.7 Battery Over-Discharge Protection
To prevent battery damage due to excessive discharge levels, the UPS control logic
automatically monitors the battery voltage and load level and switches off the output at
the predetermined battery shutdown voltage set point.