2: General Description
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TS_610_01 PowerWAVE 6000 S3 (60-120kVA) User Manual 21/10/19
mains supply. This results in the load receiving UPS protected power at all times during the upgrade process – without
interruption.
Module redundancy
A multi-module system with inbuilt module redundancy contains at least one UPS module over and above that required to
provide the specified system full load power.
For example, a PW6000 (S3) system comprising 3x 100 kW modules can be employed as a redundant module system for
a load of up to 200 kW. In this case, under normal circumstances all three modules will share the load equally and each
supply up to 66.6 kW at full load; but if one module fails, or is shut down, the two remaining modules can sustain the load
by each supplying their fully rated 100 kW. The ability to lose one module yet still supply the full load with processed,
backed-up power significantly increases the overall system reliability.
If an additional 100 kW load is added to the example system above at a later date the system will operate as a ‘capacity’
system, requiring all three modules to be available to provide a protected system; however, by adding a fourth module it
will once again operate as a redundant module system.
Once again, the PW6000 (S3) module DPA architecture enables additional modules to be connected to the parallel
system at any time without having to disturb the load.
2.4.2 Parallel UPS system operation
In a multi-module parallel system the topology and internal operation of each UPS module is identical to that described
previously for a stand-alone module. However, when operating as part of a parallel system an additional control layer is
required to cater for critical ‘system level’ control functions such as load sharing, frequency synchronisation and load
transfer, which must be observed by all the on-line UPS modules. This is achieved in the PW6000 (S3) UPS system by
connecting a ‘parallel control bus’ between the UPS modules in a daisy-chain fashion to allow them to communicate with
each other continuously and execute all necessary synchronous control operations.
System-wide load transfer operation
All the modules connected as a parallel system must be working in the same internal mode of operation at all times – i.e.
it is not permissible for one module to operate in the ‘load on inverter’ mode while the remaining modules are in the ‘load
on bypass’ mode – such a situation would almost inevitably result in damage to the modules’ inverter.
In a parallel system therefore, if you activate the
LOAD
TO
BYPASS
command
on
any one module
then all the modules will
simultaneously switch to the ‘load on bypass’ mode. Conversely, when operating on bypass if you select the command
LOAD
TO
INVERTER
on
any one module
then all the UPS modules will simultaneously transfer the load to their inverters –
provided a sufficient number of modules are operating to feed the connected load.
Inter-module frequency synchronisation and load sharing
Frequency and current sensing signals are passed over the parallel control bus to enable each UPS module to compare
its own frequency and output current with that of its neighbour. This allows each module’s control logic to effect any fine
adjustments necessary to achieve balanced conditions.
The parallel control logic always observes one of the modules as being the ‘master’ and the other module(s) 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 ‘master’ role, and the former ‘master’ module will turn off. Master/slave relationship is configured during
commissioning and should not be modified by the user.
Isolating a module from the system
If a parallel system incorporates module redundancy a module can be isolated from the system for service/repair purposes
without affecting the operation of the remaining modules or load.
Every module has a parallel (output) isolator (IA2) which can be used to disconnect the module’s output from the load bus.
When IA2 is open there is no load power being drawn from the module and it can be shut down in the normal way using
the
ON/OFF
buttons on the UPS control panel; but in this case using these buttons will shut down the associated module
only and will not cause the remaining modules to shutdown or transfer the load to bypass.
Key Point:
If a PowerWAVE 6000 S3 (60-120 kVA) module is purchased as a standalone, single unit UPS it will
require a field upgrade to make it suitable for parallel operation at a later time. For this reason, if you know that
your load is likely to expand in the future it is advisable to install a parallel-capable module at the outset.
