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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 ground) at
the rectifier and 4-wire in (plus ground) at the bypass. The output can be either 4-wire
plus ground or 3-wire plus ground depending on customer requirement.
not incorporate any galvanic isolation, input to output. The battery string comprises 240
cells (480 volts nominal) arranged in a positive string of 120 cells and a negative string
of 120 cells with the center of the series connected strings tied to system neutral, for the
80 kVA model. The 120 kVA model utilizes 144 cells on each side of the center
connection (nominal 288 volts positive and negative, for 576 volts total). 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 +390 and –390 volts DC. A pre-charge system
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 +450 and –450 volts DC. It is operated in the current mode and is
controlled using a variable modulation technique with a frequency in the range of
20 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 20 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 80 kVA system is comprised of a positive string of 120
cells and a negative string of 120 cells, each made up of twenty 12-volt battery blocks.
For the Powerware 120 kVA system, the battery strings are 144 cells positive and
negative, respectively. 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
Powerware 9335 (80 kVA and120 kVA) Installation and Operation
164201396 REV. A 071103
The unit does
5-11
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