02/02
9
1.1
Introduction:
The 7400-M series Uninterruptible Power Supply (UPS) system is
connected between a critical load, such as a computer, and its three
phase mains power supply. Being designed to furnish a well
regulated 3 phase output power supply under all rated load and input
supply conditions, the system offers the user the following advantages:
Increased power quality:
The UPS has its own internal voltage and frequency regulator which
ensure that its output is maintained within close tolerances
independent of voltage and frequency variations on the mains power
lines.
Increased noise rejection:
By rectifying the input AC power to DC power, and then converting it
back to AC, any electrical noise present on the input mains supply line
is effectively isolated from the UPS output, therefore the critical load
sees only clean power.
Power blackout protection:
If the mains power fails, the UPS continues to power the critical load
from its battery source, leaving the load immune from power
disturbances.
1.2
Design Concept
1.2.1
7400-M Module Design
This section describes an individual module’s operating principles.
The UPS basically operates as an AC-DC-AC converter (see figure 1-
1). The first conversion stage (from AC to DC) uses a 3 phase, fully
controlled SCR bridge rectifier to convert the incoming mains supply
into a regulated DC busbar.
The DC busbar produced by the rectifier provides both battery
charging power and power to the inverter section – which utilizes the
latest IGBT switching, pulse width modulation (PWM) design and
provides the second conversion phase; i.e. reconverting the DC
busbar voltage back into an AC voltage waveform.
Chapter 1 – General Description
Figure 1-1: Single Module Block Diagram
RECTIFIER
STATIC
SWITCH
INVERTER
BATTERY
Bypass
Supply
Mains
Supply
UPS
Output
Supply