Critical Power
4.2 OPERATION MODES
This section describes the different possible operation modes of the UPS explaining the function of the main modules of the UPS.
VFI (Voltage Frequency Independent) mode operation
Under normal conditions the load is permanently powered by the inverter with constant amplitude and frequency.
The rectifier, powered by the utility, supplies the
inverter and the battery-charger keeps the
battery fully charged.
Fig. 4.2-1 Energy flow in VFI Mode operation
The inverter converts the DC voltage in a new AC sine wave voltage with constant amplitude and frequency independently from the input utility power.
ECO Mode operation (Intelligent Energy Management)
When the ECO Mode is selected, and the utility power is available, the load is normally powered through the automatic bypass.
When the utility voltage is detected out of the prescribed tolerances, the load is automatically transferred to the inverter.
When the utility recovers, the load returns to the
automatic bypass after a variable time defined by the control unit.
Fig. 4.2-2 Energy flow in ECO Mode operation
The ECO Mode can be configured directly by the user for higher efficiency, considering the utility reliability and criticality of the load.
The selection between the two operation modes “VFI Mode and ECO Mode”, or switching between operation modes at required time, can be done through the UPS control panel (see Section 5.3).
In case of parallel system
ECO Mode cannot be enabled for RPA Parallel System.
Attention: A single unit equipped with a RPA - Parallel board, must be considered as parallel, thus
disabling ECO Mode.
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Automatic bypass operation
In VFI (Voltage Frequency Independent) operation mode, the load is permanently supplied by the inverter but, in case of trouble on the inverter, or when overload or short-circuit on the output occur, if the utility voltage do not exceed the admitted tolerances, the load is instantly transferred to the utility through the automatic
bypass, taking advantage of the higher short circuit power.
Fig. 4.2-3 Energy flow in automatic bypass operation
When the inverter recovers, the load will be re-transferred automatically to the inverter.
In case of parallel system
Each unit has its own bypass.
All the bypasses in the system work together, their control being managed in the same manner by all units.
The units are continuously exchanging information before taking such decision.
In case the inverter of one unit fails, its bypass remains operating.
It is excluded only if the unit is separated from the common bus by opening its output switch Q1.
Utility recovery operation
As soon as the ‘utility’ recovers, the rectifier starts up automatically supplying the inverter and the battery-charger recharges the battery.
In case the inverter has been shut-down following a complete discharge of the battery, when the utility recovers the system start-up automatically.
Fig. 4.2-4 Energy flow at utility recovery operation
When the energy stored in the battery is sufficient to ensure a minimum time of operation with the actual load, in case of a future utility failure, the load will be retransferred to inverter (if selected VFI
Mode).
In case of parallel system
When the AC input power recovers, the rectifiers will start-up sequentially according to their
number in the parallel system in order to avoid an initial inrush current.
The inverters will start-up automatically, but only when the battery has recharged enough for a
minimum runtime with the present load.
When enough inverters to supply the load have been restarted, the load will be transferred from the
automatic bypass back to the inverter bus bars.
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Manual bypass operation
The manual bypass circuit consisting of Q1 and
Q2 manual switches permits the transfer of the
load directly to the utility without interruption, leaving the UPS galvanically separated from the output load.
This type of operation is normally used when the
UPS system must be completely turned OFF for maintenance or reparation.
Fig. 4.2-5 Energy flow in manual bypass operation
Utility failure operation
In the event of a utility power failure, the
rectifier and the battery-charger turns OFF, while the inverter continues to supply the load without interruption using the energy stored in the battery.
During the battery discharge, the LCD screen displays the remaining autonomy, based on the
battery capacity and the applied load.
Fig. 4.2-6 Energy flow during utility failure operation
In the event of an extended utility failure, before the battery is fully discharged, the alarm “stop
operation” warns the user that the UPS will start the shut-down procedures when the indicated time expired (normally 3 minutes).
In case of parallel system
With parallel system for power capacity:
With the bypass utility power available as the warning “battery low” occurs on one unit, after timeout (selectable) the load is transferred to utility.
With missing bypass utility power as the warning occurs on one unit, the system starts the timeout (selectable) of “Stop operation” and then the output load shuts down.
With redundant parallel system:
As the warning battery low occurs on one unit unnecessary to support the present load, after timeout (selectable) this unit shuts down and the load is shared between the other units.
As the warning occurs on one unit necessary to support the present load, the system starts the
timeout (selectable) of “stop operation” and then the output load shuts down.
Modifications reserved
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