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7.21.2
Battery charging characteristic
See function diagram 6720 in the SINAMICS DCP List Manual.
General information
A simple battery charging characteristic curve is available if the SINAMICS DCP is used as a
battery charging device.
Principle of operation
Dependent on the battery voltage, the battery charging characteristic outputs a setpoint
charge current.
This means that towards the end of the charging process when the battery voltage is
increasing, the charge current can be reduced.
The charging characteristic can be specified with 4 interpolation points each for the battery
voltage in volts (p54210) and the charge current in amps (p54211).
After being enabled, the system follows the characteristic (p54204) until the maximum
voltage (p54210[3]) is reached. At this point in time, the charge current is reduced to zero
until, starting from the maximum voltage (p54210[3]), the battery voltage is reduced again by
the hysteresis (p54214).
A charge current can then be again output according to the settings defined by the
characteristic.
At its output (r54221) the battery charge characteristic outputs a current setpoint, which must
be interconnected with the current setpoint of the current controller (p55050).
The DCP should be operated in the closed-loop current controlled mode when applying the
battery charge characteristic.
Example
It is assumed that the battery is connected to side 2 of the DCP. The meaning of the setpoint
should then be set to "Current from side 2" (p55060 = 12) and the internal voltage actual
value at side 2 (r55506) should be interconnected with the voltage input of the battery charge
characteristic (p54203).
In addition, the approximate internal resistance of the battery (p55516) and an appropriate
smoothing time constant (p55518[1]) must be parameterized.
Notes
Here, the internal battery voltage must be used instead of the voltage actual value or the
terminal voltage of the DCP. This is the voltage with which the battery is actually charged,
without the current-dependent voltage drop across its internal resistance. As the charge
current increases, the battery terminal voltage increases as a result of the voltage drop
across the internal resistance. If the characteristic is supplied with the terminal voltage of the
battery (e.g. R55501 / r55502), then it would immediately reduce the charge current in the
reduction range of the characteristic (U > p54210[0]) as a result of the increasing terminal
voltage. This can result in a tendency to oscillate:
As a consequence, it is better to supply the characteristic with the internal voltage of the
battery (r55505 / r55506), which then takes into account the voltage drop across the battery
internal resistance. Calculating the internal voltage and the appropriate parameterization is
described in more detail in Chapter "Voltage control (Page 342)".
SINAMICS DCP
Operating Instructions, 09/2019, A5E34382853K
Operation
7.21 Technological functions
403
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