EXS
User Manual 10H52260UM60 - Rev. 1 - 10/2017
11
System Control Principle
Normal operation
Normal mode: In this condition, the UPS mains input supply is within normal limits, the rectifier and inverter operate
normally, the load is supplied by the inverter, the battery circuit breaker is closed, and the battery is in the stable
floating charge state.
(Parallel System)
Note: As the individual UPS module outputs are connected in parallel, the system checks that the
inverter control circuits are perfectly synchronized with one another and with the bypass in terms of both frequency
and phase, and that the output voltages are the same. The current supplied to the load is automatically divided
among the UPS units. A warning message appears while synchronization is in progress.
Mains abnormal
When the mains fails or is abnormal, the rectifier will stop working automatically, and the system will transfer to
battery output (through the inverter). The length of the operation time in battery mode depends on the load and the
battery capacity. During this period, if the battery voltage falls to the EOD level before the mains supply has
returned within normal limits, the inverter will stop working automatically, and the UPS operator control and display
panel will display the corresponding alarm messages. If the system uses split bypass configuration and the bypass is
normal, the system will transfer to bypass.
Mains recovery
When the mains returns within normal limits within the permissible time, the rectifier will start automatically (at this
point its output power will increase gradually) and supply the load and charge the battery again. This means that
the power supply to the load will not be interrupted.
Disconnecting the battery
To disconnect the external battery from the UPS system during maintenance, use the external isolation device. In
this condition, the battery backup function will not be available in the event of a mains failure, but none of the other
UPS functions and performance will be affected.
UPS module failure
In the event of an inverter failure, automatic inverter switch failure, or if the output fuse blows, the load will
automatically transfer to the bypass, and the output power supply will not be interrupted. Should this condition
occur, please contact your local VERTIV customer service centre for technical support.
(Parallel System)
In the event of a fault on a UPS module, it will automatically exit the parallel system. If the system
is still capable of providing the power required by the load, the remaining modules will continue to supply the load
without interruptions. If the remaining modules are no longer capable of fulfilling the power requirements, the load
will automatically transfer to the bypass.
Overload
If the inverter is overloaded or the inverter current remains outside the specifications (refer to Table 10-6) longer
than the specified time, the load will automatically transfer to the bypass without any interruption in the power
supply to the load. If both the overload and the current are reduced to a level within the specified range, then the
load will be re-transferred to the inverter. In the event of an output short circuit, the load will be transferred to the
bypass, and the inverter will shut down. The transfer is determined primarily by the characteristics of the system
protection device.
In both the situations listed above, the UPS operator control and display panel will display the corresponding alarm
messages.
(Parallel System)
The control logic system constantly monitors load requirements and controls the power supplied
by each UPS module. If an overload condition persists for longer than a pre-set period and the number of active
modules is unable to satisfy load requirements, the load will transfer to the bypass. The load is re-transferred to the
inverter if the power is reduced to a value that can be sustained by the number of active modules in the system.
