Technical FAQs

What is required value of external DC supply voltage for ATV930?

It is possible to supply ATV930 by external DC supply. The most simple calculation for DC supply voltage is to multiply ATV's AC input voltage range by sqrt(2) and you will get the DC bus voltage that ATV needs.
For example if ATV930..N4 allows AC supply 380..480V, then adequate level of DC bus is 1.41*380...1.41*480 which is 537...678V DC.

There is one more aspect to be considered, though. Motor rated voltage. As you know, ATV output voltage cannot be greater than input AC voltage, therefore bear in mind that Dc bus voltage should no be lower than sqrt(2)*rated motor voltage.
If your motor rated voltage is 400V, then DC bus voltage should be at least 565V.
So for 400V motor, the optimal level of DC bus voltage is 565V or little bit higher.

Next, ATV drives (ATV61-71, ATVprocess) up to 18.5kW have built-in precharging resistor that will limit pre-charging current, so direct connection to external DC supply is possible.
But the drives from 22kW and above do not have pre-charging resistor. Their charging current is limited by thyristors in ATV input rectifier when they are supplied by input AC voltage. But here with external DC supply there is nothing in ATV to limit the current. Therefore any drive above 22kW that is supplied by external DC voltage requires external pre-chargnig circuit. The circuit can compose of resistor+bypass relay(or contactor). The bypass relay may be controlled by ATV relay output assigned to "DC bus charged". See page 440 from ATV930 programming manual NHA80757 02/2017.
Aproximate resistance of precharging resistor to be calculated by rated DC current (Idc) and DC supply voltage (Udc).
R=Udc/Idc.
Select resistor with resistance 0.8*R ... 2*R. (Value lower than 80%R will affect capacitor lifetime, and too high resistance will prolong precharging time)
Idc=P/Udcmin where P is rated ATV power and Udcmin is minimum required DC voltage (1.41*380V in case of ATV930..N4)
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