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5.3
Functional Description
The UPS is an online double-conversion unit with a series power train. An uncontrolled
rectifier feeds a boost converter, which in turn powers the inverter. The internal static
bypass utilizes a static switch and an independent maintenance bypass switch is also
included internal to the UPS cabinet. The unit input must be 4-wire in (plus protective
ground) at the rectifier and 4-wire in (plus ground) at the bypass. The output can be
4-wire plus GND or 3-wire plus GND depending on customer requirements. The unit
does not incorporate any galvanic isolation, input to output. The battery string comprises
168 cells (336 volts nominal) arranged in a positive string of 84 cells and a negative
string of 84 cells with the center of the series connected strings tied to system neutral.
The battery is charged by positive and negative side chargers, which are powered from
the output of the boost converter.
5.3.1 Input Rectifier
The Input Rectifier is a full wave bridge uncontrolled rectifier, which produces
unregulated DC of approximately +170 and –170 volts DC. A pre-charge system pre-
charges the DC bus prior to the input contactor being closed, to control inrush current to
no higher than rated current levels.
5.3.2 Boost Converter
A Boost Converter converts the raw DC input to a regulated DC link voltage of
approximately +225 and –225 volts DC. It is operated in the current mode and is
controlled using a variable modulation technique with a frequency in the range of
7 kHz. The neutral connection is maintained from the input to the output as a fixed
connection.
5.3.3 Inverter and Filter
The inverter is a traditional (current mode controlled) hard-switched IGBT 3-phase
topology. The IGBTs are modulated by a variable frequency, current-mode control
technique at approximately 7 kHz. An output filter filters out the high frequency
switching components (line to neutral).
5.3.4 Batteries and Battery Charger
The battery for the Powerware 9320 system is comprised of a positive string of 84 cells
and a negative string of 84 cells, each made up of fourteen 12-volt battery blocks The
battery charger is divided into a positive side charger and a negative side charger, each
powered from the respective positive and negative controlled DC bus voltages. The
chargers operate automatically in the constant current or constant voltage mode based
on battery condition.
The Powerware 9320-C03 has no batteries within the UPS cabinet. The Powerware
9320-C02 contains internal batteries, however for extended runtime an external battery
Powerware 9320 (10 kVA and 20 kVA) Installation and Operation
164201416 REV. A 071103
5-11
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