Page 1.1
BP
II S, 3.00
08/96
Section I
Theory of Operation
1.1 General
The BalancedPower II–S (BPII–S) Uninterruptible Power System (UPS) presented
in this manual is a solid state, online system designed to provide high quality, continuously
filtered and conditioned ac power to computers, their peripherals and/or other critical
equipment loads. Most commonly, the UPS is configured as a single, stand-alone unit.
Three (3) power ratings are available: 15, 18 and 20 kVA. Information contained herein is
applicable to all power ratings except where specified otherwise.
A single UPS is comprised of the following basic components:
Input transformer*
Rectifier/Charger
Inverter
Static Bypass Switch
Bypass Breaker
System Control Logic and Circuitry
Digital Monitoring Panel
DC Circuit Breaker
Batteries
*
Input transformer is optional for 208–220 vac input voltages and required for 240–600 vac
inputs.
A one-line diagram in Section II shows the relationship of these various components.
1.2 Rectifier/Charger
The UPS input voltage from the utility is fed into the rectifier/charger (usually
referred to as the rectifier) which converts the ac to filtered, regulated rectifier dc link
voltage. The dc is used to power the inverter and to recharge the batteries as necessary. The
assembly consists of an input circuit breaker and a solid-state three-phase rectifier designed
to eliminate even ordered harmonics. An optional input filter reduces harmonics caused by
rectifier switching, preventing the harmonics from affecting utility distribution.
1.3 Inverter
The inverter section first uses a dc booster to increase the rectifier dc link voltage to a
dc booster link voltage.
