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Chapter 1 Overview 3

APM 300 Integrated UPS Single Module And Parallel System User Manual

A manually controlled, maintenance bypass supply is incorporated into the UPS design. It enables the critical
load to be powered from the maintenance bypass supply while the UPS is shut down for routine maintenance
and repair.

Note

When the UPS is operating in bypass mode or on maintenance bypass, the connected equipment is not protected from
power failures or surges and sags.

1.3.3

System Control Principle

Normal operation

Normal mode: It means that the UPS has normal input mains, the rectifier and inverter operate normally, the
load is supplied by the inverter, and the battery is in stable floating charge state.
(Parallel System) Note: As each 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 they have the same output voltages. Current supplied to the load is
automatically divided among UPSs. 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 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 voltage and the mains still
has not been recovered, the inverter will stop working automatically, and the UPS operator control and display
panel will display corresponding alarm messages.

Mains recovery

When the mains resumes normal within allowable time, the rectifier will start automatically (at this time its
output power will increase gradually) and supply the load and charge the battery again. Therefore, the power
supply to the load will not be interrupted.

Battery disconnection

If the battery system is taken out of service for maintenance, it is disconnected from the rectifier/charger and
inverters by means of a battery switch. The UPS shall continue to function and meet all of the specified
steady-state performance criteria, except for the power outage back-up time capability.

UPS module failure

In case of inverter failure, automatic inverter switch failure, output fuse blowout and bypass STS failure, the
load will automatically transfer to the bypass, and the output power supply will not be interrupted. In this
situation, please contact the local customer service center of Emerson Network Power Co., Ltd for technical
support.
(Parallel System) In the event of a fault in a UPS module, it will automatically exit from the parallel system. If
the system is still capable of providing the required load, the remaining modules will continue to supply the
load with no interruption. If the remaining modules are no longer capable of fulfilling 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 11-6)
longer than the specified time, the load will automatically transfer to the bypass without power interruption. If
both the overload and the current are reduced to a level within the specified range, then the load will be
transferred back to the inverter. In case of output short circuit, the load will be transferred to the bypass, and