Samlexpower samlexpower SCC-30AB, Руководство пользователя

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18 | SAMLEX AMERICA INC. SAMLEX AMERICA INC. | 19
SECTION 4 | Principle of Operation & Features
Through PWM control, the Switch converts constant Short Circuit Current (I
SC
) at
its input to controlled average current at its output by varying the Duty Cycle. The
average value of output current of the Switch is equal to the constant input value of
Short Circuit Current (I
SC
) multiplied by the Duty Cycle. Fig 4.1 above shows an example
where 2.7A constant input Short Circuit Current (I
SC
) is reduced to average of 25% or
to 0.675A by switching the 2.7A constant Short Circuit Current (I
SC
) ON and OFF at 25%
Duty Cycle.
PWM Charging in SCC-30AB
Battery charging is a current based process. Current fed to the battery results in
re-charging of the cells and consequent rise in battery voltage. Controlling the
current will control battery voltage. For 100% return of capacity, and for prevention
of excessive gassing and sulfation, the battery charging voltage is required to be
controlled at the specified Voltage Regulation Set Points for Absorption, Float and
Equalization Charging Stages for different battery types. Battery can, thus, be charged
at the specified Voltage Regulation Set Points by PWM of the charging current
through control of Duty Cycle as explained above. The controller checks the battery
voltage and updates the Duty Cycle regularly at a very fast rate. The Duty Cycle is
proportional to the difference between the sensed battery voltage and the Voltage
Regulation Set Point. Once the specified Voltage Regulation Set Point is reached, it
is kept steady - rise in voltage is compensated by reducing the average current by
reducing the Duty Cycle and fall in voltage is compensated by raising the average
current by raising the Duty Cycle. These fast updates on battery voltage measurements
and Duty Cycle corrections ensure charging of the battery at the specified Voltage
Regulation Set Point with minimum deviation of +/- 50mV.
Optimum PWM Frequency: The PWM frequency can range from tens of Hz to around
1000 Hz. At higher frequencies, the time period between the cycles is lesser and is not
sufficient to complete the electro-chemical reactions. At lower frequencies, the rise
times of the charging pulses are lower which results in higher gas bubble formation
resulting in lowering of active surface area and increase of internal impedance.
In SCC-30AB, frequency of 300 Hz is used for optimum charging performance.
Charging Algorithms
Notes:
1. For proper understanding of the charging algorithm, please read Section 3 –
General Information: Batteries.
2. For purposes of explanation given in Fig. 4.2A / 4.2B, it is assumed that there is no
load on the battery during the day when charging is taking place. There is small
lighting load at night, which is switched OFF during the day.