1- INTRODUCTION
The static uninterruptible power supply system (UPS)
supplies the connected consumers continuously and reliably with energy. The
voltage and frequency constancy is
maintained regardless to sags and failures of the mains according to the
specified data. Accumulator batteries are used as an energy storage medium.
2-SINGLE UPS SYSTEM WITH
MAINS BYPASS
2.1 CONFIGURATION
The UPS system with mains bypass consists of 1
rectifier, 1 inverter and 1 electronic changeover unit EAN with the static
switches EA and EN. In addition, 1 manual service bypass switch with
overlapping action is installed. A transformer or a mains voltage regulator
(stabilizer) may optionally be used in the bypass mains line.
2.2 PRINCIPLE
DIAGRAM
2.3 DESCRIPTION
OF OPERATION
The UPS system may operate in four different modes.
The priority for the different modes is the following:
1. Normal operation
2. Battery operation
3. Bypass operation
4. Standby/Off
1. Normal
operation
The AC input (rectifier-mains) is fed to the phase
angle controlled rectifier via a matching transformer or a mains choke. The
rectifier compensates mains voltage fluctuations as well as load deviations,
and maintains the DC voltage constant. The superimposed AC- voltage component
(ripple) is reduced by means of a smoothing circuit. The rectifier supplies the
inverter with energy and secures that the connected battery is kept on standby
(float charge and boost charge depend on charging condition of the battery and
on the battery type).
The downstream inverter converts the DC voltage by
means of optimized sine wave pulse width control (PWM) into AC voltage and
supplies the load via the static switch EA.
2. Battery
operation
In the event of power sags or failures the inverter is no longer supplied with power by
the rectifier. The battery, which is connected to the DC intermediate circuit,
is called up automatically and without interruption to supply the current.
The discharging of the
battery is signalled. The battery voltage drops in function of the duration and
the magnitude of the discharge current. The voltage drop is compensated by the
inverter, whereby the UPS output voltage is kept constant.
If the limit of discharge of the battery is nearly
reached an alarm is given. If the limit of discharge is reached the system
changes automatically to bypass operation, if the bypass mains is available and
within the tolerance range. If the bypass mains is not available or not within
the tolerance range the system will shut down automatically.
On mains recovery or on emergency power generation
with diesel generator the rectifier immediately resumes its function of
supplying the inverter, and at the same time of charging the battery, if the
UPS system is programmed for AUTOSTART at mains recovery. If the system is not programmed for AUTOSTART it has to be restarted
manually see "Start / Operation" .
Depending on the depth of discharge of the battery
the charge current is limited by means of the battery current limiter.
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