20
4.2. DEFINITION AND STRUCTURE
4.2.1. Structural diagram.
To describe the operating principle, it is taken as a reference and
examp
le the single line diagram of Fig. 25 and 26, corresponding to
UPS
with three-phase input and output setting, one with basic
structure and the other one with separate bypass line.
All the equipment works and oper
ates in the same way, although
they have common line or separate static bypass.
4.3. UPS FUNCTION STAGES.
This UPS series is structured in the following stages:
• I/O EMI filters.
• Rectifier-PFC (AC/DC).
• Batteries.
• Inverter (DC/AC).
• Static Bypass.
• Maintenance or manual Bypass.
• EPO emergency shutdown.
• Control panel.
• Control and communication Software.
4.3.1. I/O EMI filters.
EMI filter is a three phase
low-band filter, whose function is to
attenuate and cancel all the radio frequency perturbations. The
filter performs in a bidirectional way:
• It cancels the perturbations that come from the line and
protect the UPS control circuits.
• It avoids the possible radio electrical perturbations that the
UPS generate through the line and affect other equipment
connected to it.
4.3.2. Rectifier-PFC stage (AC/DC).
Constructive parts:
•
Input protection and switch
: it is the particular protection of
the PFC rectifier.
•
Current sensor
: it uses alternating current transformers to
measure and control the input current, to get a THDi < 3% at
full load condition and even < 1% depending on the quality of
mains.
•
“T” filter
: it is used to attenuate the current ripple caused by
the PFC switching.
•
IGBT's three phase bridge
: it will be used to make the AC/
DC conversion with the lowest distortion and highest efficiency.
To do that, it is used the Trench-gate IGBT technology of 4th
generation.
•
Input chokes
: They are used by the PFC rectifier as energy
storage elements (in switching times), for the AC/DC
conversion.
•
DC Bus
: it is used to filter the DC needed for the correct
operation of PFC converter and inverter.
4.3.3. Batteries.
This UPS series has a battery set that stores energy during the
normal operating mode (present mains) and they are discharged
during the emergency operation (mains fault), keeping the critical
loads running during the required time.
Batteries are sized to supply full power to the assigned critical loads
during the back-up time for any load condition. Standard batteries
are sealed Lead Acid, maintenance free and VRLA technology.
Each cell or cell group (battery block) are duly marked in a
permanent way, with polarity indication, voltage and safety
warning required by th
e standard.
Cells are duly assembled and electrically connected. Battery set is
protected by means of a fuse holder with ultra fast fuses, ready for
the described conditions in section
«
4.3.2. Rectifier-PFC stage
»
.
In normal operation (mains present and charged batteries), the
battery set is working on floating voltage.
As an option the battery set of Pb-Ca or Ni-Cd can be assembled
in a cabinet or rack separately from the equipment, shared for
systems made of two UPSs in parallel.
4.3.4. Inverter stage (DC/AC).
Constructive parts:
•
DC Bus
: it is used to filter the DC and it is in charge of
interconnecting the PFC and Inverter through the protection
fuses.
•
IGBT three phase inverter bridge
: it is equal to the PFC
stage but in counter way, it is in charge of making the DC/AC
conversion with the lowest distortion and highest efficiency. It
is also using the Trench-gate technology of 4th generation.
•
Current se
nsor
: as it has been described before, in this case
conventional AC currents sensors are also used (current
transformers) for measurement and control the output current of
the inverter to get a total harmonic distortion at the output
voltage lower than 1% in full load conditions.
•
Output chokes
: Use identical solution as the input. These
chokes are used by the inverter as energy storage elements (in
switching times), for DC/AC conversion.