90 | SAMLEX AMERICA INC.
SECTION 5 | Battery Charging in Evolution™ Series
INFO
Please note that as the unit is Bi-Directional with a common Converter Section as explained
above, it cannot work as inverter and charger at the same time
During “Charging Mode”, the internal Transfer Relay is energized when AC input power from Grid / Generator is
within the programmed limits of voltage and frequency and the following actions are initiated:
• AC input power is fed to the Common Converter Section for conversion to DC voltage to charge the batteries
• AC input power is simultaneously passed through to the AC loads
5.1.2 Basics of PWM (Pulse Width Modulation) Based Charging Process
5.1.2.1 AC input power is fed to the Primary Winding of the Isolation Transformer. The voltage on the Secondary of
the isolation Transformer is stepped down and fed to input of H-Bridge Converter that uses four N-Channel Mosfet
Switches. The output of the H-Bridge is fed to the battery / battery bank. PWM (Pulse Width Modulation) technique is
used for the charging process. PWM frequency is 30 kHz
5.1.2.2 The two High-Side Mosfet Switches of the H-Bridge are kept OFF and their Body Diodes are used for full-wave
rectication of the stepped down AC input voltage. The average / mean value of battery charging current will vary
between 0A and a Positive peak value in the form of DC Wave resembling sine wave. The charging current displayed
by the EVO-RC Remote Control will be the average / mean value of the above DC Wave
5.1.2.3 The two Low-Side Mosfet Switches of the H-Bridge are switched ON / OFF together at PWM frequency of
30 kHz with variable “Duty Cycle” proportional to the desired value of charging current. When the two Low-Side
Mosfets are ON for period determined by the “Duty Cycle” set by the micro-controller, the Secondary Winding will be
short circuited and magnetic eld proportional to the short circuit current will be created by the winding. When the
two Low-Side Mosfet Switches are switched OFF, short circuit of the winding is removed resulting in collapse of the
magnetic eld and generation of induced voltage pulses at PWM frequency of 30 kHz with a value = - L di/dt where
“L” is the Inductance of the winding and “di/dt” is the rate of decay of Short Circuit Current. Thus, higher Duty Cycle
will produce induced pulses with higher voltage. When the voltage of the induced pulses is > the battery voltage,
charging current pulses will be produced. The value of charging current pulses will be proportional to the difference
of voltage between the voltage of the induced pulses and the battery voltage
5.1.2.4 During the Bulk Stage of charging (Section 5.7.1.1), the average / mean charging current set by programming
parameter “BULK CURRENT” [See section 4.4.2.1 of EVO-RC-PLUS Remote Control Manual] is held constant by
controlling the “Duty Cycle” of the 30 kHz induced pulses.
INFO
When charging starts, the charging current is NOT increased to the programmed value of
parameter BULK CURRENT immediately but is gradually ramped up to this value
5.1.2.5 During Absorption Stage (Section 5.7.2), Float Stage (5.7.3) and Equalization Stage (5.8.2.3), the battery
voltage is held constant indirectly by controlling the “Duty Cycle” of the 30 kHz induced pulses. For example, if the
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