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Basics: Direct current links

Matthias Beetz, Baumüller Nürnberg GmbH

Read min.

Direct current links

A DC link is an element connected between multiple power supplies. It can both couple these power supplies and act as a buffer storage for electrical energy. In practice, it is used to synchronize frequencies of different power supplies, for example. Its industrial use in electric drives offers further advantages, because it helps to conserve energy. Since DC links can act as an energy store, they can also be operated as a generator, e.g. to store braking energy for other uses. They can also be used to mitigate power peaks.

The following glossary entry covers:

Definition – What is a DC link?

A direct current link refers to an electrical module which can temporarily store energy. There are many possible purposes for this: On the one hand, a DC link can be used to couple multiple electrical power supplies by placing incoming and outgoing converter units (of servo and frequency controllers) around the DC link, with the DC link then effectively acting as an adaptive intermediate level. On the other hand, energy can also be temporarily stored in the DC link, where it remains available on demand. This energy can be generated directly in the process. One example is the servo motor: Here, the energy generated in braking processes can be temporarily stored in a corresponding capacitance unit in order to release it again later in acceleration processes.

Related terms

  • DC link voltage: This is the voltage that prevails in DC links. This voltage fluctuates due to the continuous input and output of energy and is adjusted in each case by means of the adjacent converters.
  • DC link capacitor: This is the actual energy storage device.
  • Pre-charging circuit: In a DC link, this circuit consists of electrical resistors. These are bridged when the DC link capacitors are fully charged.

Practical examples in industry

In industry, DC links can improve cost efficiency when using electric drives, such as servo motors. In such applications, short-interval braking and acceleration processes usually follow one another in quick succession. The braking energy can be absorbed and fed into a new acceleration. This makes the overall system more energy-efficient and therefore more cost-effective. There are also many other advantages, depending on the design.

Potential cost savings in the application example

DC link capacitance unit for b maXX 5000 series

The following is an example of an actual DC link unit provided to illustrate the specific advantages of DC links in operation. The Baumüller DC link capacitance unit for the servo controllers of the b maXX 5000 series allow the buffer storage of the braking energy required during the operation of the servo motor. This energy can then be released again for later acceleration processes. This reduces the energy consumption of the overall process, thereby reducing costs in very appreciable way. There are also other advantages, such as:

  • Leveling the peak load: This offers a major cost advantage. The reason lies in the framework agreements usually concluded with energy supply companies. High consumption peaks raise the prices of such agreements. By using DC links, energy can be held in reserve to mitigate the peak loads. This reduces costs relative to the individual electricity supply company.
  • Lower thermal radiation: Increased space requirements also mean added costs. By lowering thermal radiation, cooling units can be used with more compact designs, which saves space.
  • Further space savings: The control cabinet and feed unit can also be designed to be smaller, freeing up additional space. 

In addition, the energy stored in a DC link enables a controlled system shutdown in the event of faults, such as power failures. This eliminates the need for an independent power supply (UPS), which prevents damage resulting from sudden failures during emergencies. In the big picture, this means yet another potential source of cost savings.


The use of DC links in electrical drives offers an enormous savings potential. On the one hand, DC links increase energy efficiency, because energy that is already generated in braking processes, for example, can be used as a generator and stored temporarily before being released again for acceleration. In addition, they effectively save space by reducing the space required for the control cabinet, feed unit, and cooling unit. In addition, the temporarily stored energy can be used to ensure a controlled system shutdown in the event of an emergency in order to prevent damage. DC links also eliminate the need for an additional independent voltage supply for power failures.

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Matthias Beetz
Training Engineer Academy I Baumüller Nürnberg GmbH

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