Mains choke, function of DC bus supplied drive controller

Question:

What do mains chokes of frequency inverters serve for?

Answer:

Uncontrolled input rectifiers of frequency inverters rectify the AC voltage for the DC bus. As an energy store the DC bus has electrolytic capacitors. By the input rectifier of the frequency inverter the DC bus is loaded to the peak value of the mains voltage, and from the mains current is taken in the peak of the mains voltage. According to the internal resistance of the supplying mains high peaks occur. These peaks lead to distortions in the mains voltage.

Mains chokes in the supply cable extend the current flow time and reduce the current peaks in the mains. Consequently the reactions of system are also reduced.

A positive side effect: The low current peaks increase the life time of the DC bus capacitor considerably.

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