DC link capacitor

from Wikipedia, the free encyclopedia

An intermediate circuit capacitor is an electrical capacitor in the intermediate circuit of converters . Its task is the energetic coupling of several electrical networks with one another on a common DC voltage level .

In an electric locomotive , for example, electrical energy from the traction current AC voltage network (f = 16.7 Hz) can be fed into the intermediate circuit via a four-quadrant controller. The AC mains voltage is converted into a DC voltage (the intermediate circuit voltage ). This energy can in turn be converted into an alternating voltage of variable frequency (typically 0 to 150 Hz) for the traction motors via a pulse- controlled inverter while driving. Since the pulse-controlled inverter also works as a four-quadrant controller , the energy flow can also be reversed (e.g. when braking, driving down a hill). In addition to the conventional intermediate circuit capacitors , a suction circuit is also housed in traction converters .

Aluminum electrolytic capacitors are generally used in power electronics because they have a very high power density. Foil capacitors with polypropylene foils (PP) are also increasingly being used, as these have the following advantages over electrolytic capacitors:

  • About a factor of 3 higher dielectric strength (series connection is no longer necessary up to 2 kV)
  • Temperature resistance down to −40 ° C can be achieved
  • low Equivalent Series Resistance (ESR)
  • much higher reliability (also due to self-healing properties)
  • AC voltage-proof (can therefore also be used for reactive power compensation, for example )