Technical FAQs

# Do we need external pre-charging circuit for drives above 22kW when supplied to DC bus from solar panel?

The purpose of external pre-charging circuit is to limit the charging current for all drives that do not have buil-in precharging resistor (means all drives of sizes D30N4 an above, and all drives of sizes D15M3 and above). Precharging circuit limits the current when ATV (with empty DC bus) is connected to a DC supply device that already has voltage on its ouptut.
However if your DC supply (solar panel) can limit the current that is delivered to discharged DC bus, then you do not need precharging current for drives above 22KW (n4) or above 15kw (M3).
But consider the first moment, ATV with empty DC bus (Udc=0) is connected to a solar panel that gives for example Uo=500V DC on its output. Charging current I=(U0-Udc)/R
Where "R" in your circuit consist of : resistance of the wires (practically zero) + resistance of DC bus capacitors (also zero) + internal resistance of solar panels (??)
So without external circuit, solar panel will be loaded like in case of short-circuit. Can your solar panel limit this short circuit current so that the short circuit current value is below the ATV rated DC current?
I would say better not to do such an experiment. But you may check the datasheet of your solar panel. This information about short-circuit current should be available. Second point of view is, that even if your solar panel short-circuit current is below ATV rated DC bus current, ask solar panel manufactures if this current affects solar panel lifetime.
Rated DC current is calculated as P/Udcmin where P is drive power, Udc min is dc voltage that corresponds to min AC supply. For N4 drives, Uac min=380V, hence Udcmin is 537V (=sqrt(2)*380V)
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