Is it mandatory to install an External Pre-charging circuit for Variable speed drives above 22kW when primed directly to the DC bus from solar panels?

The purpose of the external pre-charging circuit is to limit the charging current for all drives that do not have built-in pre-charging resistors (which means all drives of sizes D30N4 and above, and all drives of sizes D15M3 and above). The pre-charging circuit limits the current when an ATV (with an empty DC bus) is connected to a DC supply device that already has voltage on its output.
However if your DC supply (solar panel) can limit the current that is delivered to the discharged DC bus, then you do not need recharging current for drives above 22KW (n4) or above 15kw (M3).
But consider the first moment, ATV with an 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 consists of : the resistance of the wires (practically zero) + resistance of DC bus capacitors (also zero) + internal resistance of solar panels (??)
So without an external circuit, solar panels will be loaded like in case of a 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. The second point of view is, that even if your solar panel short-circuit current is below ATV-rated DC bus current, ask solar panel manufacturers if this current affects the solar panel lifetime.
Rated DC current is calculated as P/Udcmin where P is drive power, and Udc min is DC voltage that corresponds to min AC supply. For N4 drives, Uac min=380V, hence Udcmin is 537V (=sqrt(2)*380V)

Publié pour: Schneider Electric Belgium