UPS471-02-00 PW9000DPA User Manual UK Dated 06/08/14
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2: General Description
2.3.4 Multi-module parallel system operation
As described above, the PowerWave 9000 cabinets are designed to
accommodate between one and five UPS power modules. Each module
has an individual output power isolator (IA2) which connects the module's
output to the cabinet’s output power terminals. This enables an individual
module to be disconnected from the load supply for maintenance or
repair purposes.
Under normal conditions all the modules within the cabinet are turned on
and operating in parallel to provide the cabinet’s rated output.
‘Capacity’ versus ‘redundant module’ system
The paralleled UPS modules can be operated as either a
capacity
or
redundant
module system.
The difference between the two is that a ‘capacity’ system is rated such
that ALL the power modules are required to furnish the specified full load
power, whereas a ‘redundant-module’ system is designed with one (or
more) modules over and above that required to supply the full load.
In a redundant-module system it is therefore possible to lose one (or
more) power module without disrupting the load, whereas this is not the
case in a capacity system where the loss of one power module would
automatically transfer the load to the bypass supply.
Parallel control bus
All the UPS power modules within a cabinet are connected to a parallel control bus which carries various inter-module
control signals used for frequency synchronisation, load sharing etc. By using sensing signals passed over the parallel
control bus, each power module can electronically compare its own frequency and output current with that of its
neighbouring module and carry out fine adjustments to achieve balanced conditions.
The module control logic always observes one of the power modules as being the ‘master’ and the others as ‘slaves’.
However if the ‘master’ module goes faulty at any time the next module in the chain (a former ‘slave’) will immediately take
over the role of master and the former master module will turn off.
Multi-cabinet parallel system
To further expand the overall UPS system capacity, several (up to ten) PowerWave 9000 cabinets can be connected
together to operate as a ‘multi-cabinet’ parallel system. This is achieved by connecting each cabinet’s output power
terminals in parallel at an external load distribution panel and linking together the parallel control bus in each cabinet to
effectively provide a single parallel control bus that is connected to every power module in the system – see Figure 2.9.
Taken to its limit, a system comprising ten fully populated DPA-250 cabinets would result in a UPS system rating of
2500kW; however, such large systems are rare and a typical multi-cabinet installation will contain far fewer than the
maximum ten cabinets.
It is essential that any installed UPS power protection system can be expanded to meet a growing load demand without
compromising the existing load supply.
This condition is easily managed by a PowerWave 9000 system which, due to its ‘hot-swappable’ design, makes it
possible to fit an additional power module to a DPA-150 or DPA-250 cabinet if it is not already fully populated, or add a
further cabinet to an existing UPS system without disrupting the load supply.
Note:
Every standard PowerWave 9000 cabinet is supplied with all the features required for parallel operation to eliminate
any need for time-consuming or expensive upgrading on site.
WARNING:
The on-line mode must always be used for critical load protection.
Figure 2.8 Single cabinet with five
parallel power modules
Parallel Control Bus
Fully populated cabinet
with 5 parallel power
modules connected to a
parallel control bus.
Operator Control Panel (for each Module)