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SECTION 3 |
General Description
This unit is a Pure Sine Wave Bi-directional, Single-Phase Inverter / Charger
with a Transfer Relay that operates either as an inverter OR as a smart
battery charger. It uses a common Converter Section that can work in two
directions – in one direction it converts external AC power to DC power to
charge the batteries (Utility / Generator Mode) and in the other direction,
it converts DC power from the battery to AC power (Inverter Mode). This
allows the same power components to be used in both directions resulting
in high-energy transfer efficiency with fewer components. Please note that
it can not work in both the directions at the same time (i.e. it can not work
as an inverter and as a charger at the same time).
A high performance micro-controller and Pulse Width Modulated (PWM)
conversion circuits are used for the above implementation.
Components of The System
It consists of 3 Sections – Inverter Section, Battery Charger Section and
Transfer Relay Section. The unit is fed with the following inputs:
• External AC input power source – can be the Utility or a generator
• DC Battery Source - Two versions of G4 Series are available. One
version is for a 12 vDC battery input (G4-2012A) & the other is for a
24 vDC battery input (G4-2524A & G4-3524A)
• Additional external charging source like Solar Charge Controller / AC
charger of up to 50A capacity. The output of the external charging
source is routed through this unit and operates in parallel with the
internal charger. The internal charging current is controlled to ensure
that the combined current fed to the battery does not exceed the
programmed Bulk Charging Current. This improves the life of the
battery.
Inverter Section: Is a heavy-duty, continuously working, micro-controller
based inverter generating a Pure Sine Wave output of 120 vAC, 60 Hz
from the DC Battery Source. It is able to supply AC power to various types
of AC loads such as resistive loads (heaters, incandescent lamps etc) or
reactive loads (motors, air conditioners, refrigerators, vacuum cleaners,
fans, pumps, Switched Mode Power Supplies (SMPS) used in audio / video
equipment and computers, etc.).
Principle of working of the Inverter Section: The low DC voltage
from the DC Battery Source is inverted to the AC voltage in two steps.
The low DC voltage from the DC Battery Source is first converted to low
frequency (50 Hz or 60 Hz), low voltage synthesized sine wave AC using an
H-bridge configuration and high frequency PWM (Pulse Width Modulation)
technique. In order to create this low voltage, low frequency synthesized
sine wave, a reference low frequency sine wave and a high frequency
carrier wave are generated. The low frequency, low voltage synthesized
sine wave is then stepped up to 120 vAC pure sine wave voltage using a
low frequency Isolation Transformer and filtration circuit. This type of DC
to AC inversion is called Hybrid Type – a combination of low frequency and
high frequency implementation.
Soft Start in Inverter Mode: The inverter design incorporates "Soft
Start" feature with the following advantages and protections:
-
When the inverter is turned on, the output voltage ramps up gradually
from around 40 vAC to 120 vAC in around 350 ms. This reduces
otherwise very high starting inrush current drawn by AC loads like
Switched Mode Power Supplies (SMPS) and motor driven loads like
General description &
Principles of Operation
fans, pumps, compressors etc. This will result in lower motor inrush
current (which typically can be up to 650% of the full load current of
the motor), which means lesser mechanical stresses, wear and tear
and increased lifetime of the motor, coupling and fan. Additionally, the
impact on the load side components is greatly reduced, meaning less
likelihood of causing problematic voltage drops during starting.
-
When high power load or load with high starting / inrush surge is
switched on when the inverter is running and supplying the full rated
voltage, the output voltage will momentarily dip and ramp up again
gradually. This will have the same effect as described above
-
Reduction in output voltage and consequent reduction in output
current due to high inrush surge conditions imposed by certain
loads prevents the inverter from premature failure due to excessive
overloading
Transfer Relay Section: Is used to either feed AC power to the Battery
Charger Section and at the same time, pass through the AC power from
the external AC input power source to the load (As long as the external
AC input power source is available and is within the programmed limits
of voltage and frequency) or to transfer the load to the Inverter Section (In
case of loss of the external AC input power source or if this source is not
within the programmed limits of voltage and frequency). Typical transfer
time is 20 milliseconds. Heavy duty 80A, SPDT Transfer Relay is used for
reliable transfer of up to 300% surge power and for Neutral to Ground
Bond Switching.
battery Charger Section: The Battery Charger Section of these units is
a powerful, micro-controller based, 4 Stage Charger - 80A for the 12v,
2000vA version and 70A for the 24v, 2500vA and 3500vA versions. The
same Isolation Transformer and the H-Bridge configuration are used to
work in the reverse direction – rectify the AC voltage from the Primary
AC Power Source to controlled low voltage DC to charge the DC Battery
Source. That is why it is called a Bi-directional device. 4 Stage Charging
Algorithm is used – Bulk, Boost, Equalization and Float. (The Equalization
Stage is selectable). Equalization Stage is desirable for the proper health
of Wet Cell Batteries. Further, the charging voltages and currents are
programmable to take care of a wide range of battery types like flooded,
AGM, Gel Cell, Lead Calcium, etc.
Please see details under section 4 titled "Battery Charging in g4
series" and section 7 titled "setting Menu and display screens".
Modes of operation
Utility Mode: As long as the external AC input power from the utility is
available and is within the programmed limits of voltage and frequency, it
is passed through to the AC load through the Transfer Relay Section. At
the same time, the Battery Charger Section converts the external AC input
power from the utility to DC power to charge the DC Battery Source. In
case the utility fails, the load is transferred to the inverter in around 20 ms.
Generator Mode: As long as the external AC input power from the
generator is available and is within the programmed limits of voltage
(frequency is not qualified in this Mode), it is passed through to the
AC load through the Transfer Relay Section. At the same time, the Battery
Charger Section converts the external AC input power to DC power to
charge the battery (charging will be interrupted during the period when
generator freqency is not within the range of 45 to 65 Hz due to overload
distortion). In case the generator fails, the load is transferred to the
inverter in around 20 ms.
SAMLEX AMERICA INC. | 9
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