Chapter 1 Product Introduction 3
Liebert ITA 16kVA/20kVA User Manual
1.4 Operating Principle
The operating principle of the UPS is shown in Figure 1-3.
I/O filter
Rectifier/PFC
Inverter
DC/DC charger
Battery
Mains
GND
GND
Bypass
Output
Figure 1-3 Operating principle
1. The UPS is composed of mains input, I/O filter, rectifier/PFC, DC/DC charger, inverter, bypass, battery and UPS
output.
2. When the mains is normal, the rectifier will start, and the DC/DC charger will charge the battery strings. Before
turning on the UPS, the output voltage is the bypass voltage. After turning on the UPS, the electronic transfer switch
connects the inverter to the load, and the mains supplies DC power to the inverter through the rectifier/PFC circuit.
The inverter then inverts DC power to pure sine wave AC power and supplies AC power to the load through the
electronic transfer switch.
3. When the mains is abnormal, the rectifier/PFC circuit boosts the battery voltage and supplies it to the inverter. The
inverter then converts it into pure sine wave AC power, and supplies AC power to the load through the electronic
transfer switch.
4. After the mains returns to normal state, the UPS will automatically switch to Normal mode from Battery mode, the
mains power supplies DC power to the inverter through the rectifier/PFC circuit, and then the electronic transfer
switch supplies DC power to the load.
1.5 UPS State And Operation Mode
The UPS state and operation modes include: Normal mode, Bypass mode, Battery mode, ECO mode and Fault state.
For the description of indicators in this section, refer to
Chapter 3 Operation And Display Panel
for details.
1.5.1 Normal Mode
When the mains input is normal, the load is powered with voltage-stabilizing and frequency-stabilizing power supply
by the mains after processing of the rectifier and the inverter, and meanwhile, the operation mode that the charger
charges the battery is the Normal mode. In Normal mode, the inverter indicators are on (green).
1.5.2 Bypass Mode
If the overload is overtime, inverter or rectifier fails during the UPS operating in Normal mode, the UPS will switch to
Bypass mode, and the load is powered by the bypass source, which comes directly from the mains input; if the
rectifier is normal, the internal charger will charge the battery. In Bypass mode, the inverter indicators are off.
Note
In the event of the mains failure or mains voltage exceeds the specifications in Bypass mode, the UPS will shut down and stop the
output.
