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1.2.1 DESCRIPTION OF BLOCKS
RECTIFIER:
In LION Series UPSs, a DSP controlled IGBT rectifier with PWM technique is used to increase
input power factor (PFC) and to decrease input current harmonics (THDI).
The IGBT rectifier accepts 3-phase AC input and produces a dual polarity DC voltage for both supplying the
inverter and charging the batteries.
BATTERIES:
Batteries are used as reserve DC power supply for the Inverter in case of mains failure. In LION
Series, batteries are connected in series with a center-tap output to obtain a dual polarity DC supply.
Batteries are discharged by the inverter during mains failure. The discharged batteries are re-charged by the
IGBT Rectifier on a constant voltage / current limiting basis, if AC mains power is available.
INVERTER
: It is manufactured by using the latest IGBT and DSP (Digital Signal Processing) technologies,
and Pulse Width Modulation (PWM) technique. The Inverter converts the DC BUS voltage supplied by the
IGBT Rectifier and / or the batteries into a well regulated, fully digital controlled 3-phase AC voltage with fixed
voltage and frequency.
The output of the inverter is used to supply the critical loads connected to the UPS output.
STATIC TRANSFER SWITCH (STATIC BYPASS):
This is an electronically controlled transfer switch, which
enables the critical load to be connected either to inverter output or to by-pass power source. During normal
operation, the load is supplied by the inverter output, but in case of an overload or a UPS failure it is
automatically transferred to the bypass source without any interruption.
MAINTENANCE BYPASS SWITCH (MBS):
This is a manually controlled mechanical switch, which is used to
supply the critical load, using the bypass source, when the UPS is shut down for maintenance or
troubleshooting purposes.
The load is unprotected against mains supply disturbances and black-outs when it is connected to either static
or maintenance bypass supply.
1.2.2. OPERATING CONDITIONS OF UPS
UPS may be in one of the following operating conditions:
A. Normal Operation (If Mains supply is available):
All fuses and power switches are closed (except the Maintenance Bypass Switch), and the load is supplied by
the Inverter Output. During normal operation, the Rectifier supplies DC power to the Inverter and charges the
Batteries at the same time.
B. Battery Operation :
The Batteries are connected to the Rectifier output. In case of a mains failure (mains power outage or AC
input voltage out of tolerance), the Rectifier stops operating and the DC voltage necessary for the inverter
operation is supplied by the batteries. Therefore the AC voltage output supplying the critical load is not
interrupted, until the batteries are fully discharged. At the end of the discharging time the inverter is turned off
and it start again automatically, together with the rectifier, when the mains power is restored, and the UPS
returns o normal operation. For UPS with a split bypass source, at the end of discharging time, static transfer
switch transfers the load to the split bypass source without interruption if the split bypass source is available
and in acceptable tolerances about voltage and frequency, as still the rectifier input is not available.
The Rectifier is also turned off and inverter operates on batteries during automatic or manual battery test
procedure.
C. By-Pass Operation :
If the Inverter output is overloaded or in case of a problem in the UPS, the static switch transfers the load to
the bypass supply without any interruption, provided that the bypass supply is available and within the
tolerated limits regarding voltage and frequency. At the end of the overloading period, if the fault condition is
restored, static switch transfers the critical load again to the inverter output. Note that, during operation from
the bypass supply, the critical load may be effected by any possible disturbances or power failure in the
bypass supply.
