DC link connection: Braking energy cleverly stored temporarily

Baumüller has increased its focus on the development of energy-efficient drive concepts for many years. The efficient use of resources is also evident in the b maXX servo drives, which can be connected to each other via a common DC link. For example, during braking, the system’s kinetic energy can be converted into electrical energy and distributed to other axes by the DC link system.

Application in the recycling industry

In a twin-shaft shredder, for example, the recovered braking energy from the first shredder shaft can be used to drive the second shaft. This principle can be used in both normal and reverse operation.

Application in plastics processing

The module system combined with a mono unit in a DC link system is useful, for example, for the electrification of a small number of axes in combination with a powerful drive axis. The starting point is often an already implemented servo-hydraulic drive, which is supplemented by additional electric axes. In this case, the large, powerful mono unit is linked directly to the module system via intelligent connection technology. This saves space in the control cabinet and is easy to implement, as both unit types use the same firmware. The degree of electrification of servo-hydraulic injection-molding machines can thus be increased cost-efficiently thanks to the limited engineering work required and the elimination of a separate power supply.

How a DC link connection works

Energy efficiency through energy exchange

When a motor is braked, energy is fed back into the servo drive's DC link. The DC link system thus transfers the regenerative braking energy of the motor as motor energy for another servo drive. This means that overall, less energy is required from the power grid.
Tip: To save even more energy and costs, one shredder shaft in a twin-shaft shredder could additionally accelerate as soon as the other slows down.

Temporary store saves brake resistors

When a motor is braked, energy is fed back into the servo drive's DC link. To protect the servo drive from overvoltage, a braking resistor converts the surplus energy into heat. The energy is "burned" in the process.
A DC link system allows surplus energy to be divided between two or more b maXX servo drives. This means that brake resistors can be designed smaller or omitted entirely. This saves space and reduces costs for the control cabinet and energy.

Energy buffer for controlled shutdown of the system

The DC link system also impresses in the event of malfunctions. In the event of a power outage or malfunction, the stored energy can be used to shut down the system in a controlled manner. The drive axles can thus be moved to a defined position depending on the available residual energy and the energy requirement. This prevents damage and accelerates a machine restart considerably. This function is integrated directly into the drive and can immediately execute this response in the event of a fault, e.g., to prevent damage to the mechanics.
In addition to increasing system availability, the energy buffer can also remove the need for an independent power supply.

How can servo drives be connected to a DC link system?

Implementing a DC link connection is very simple. Since the mono units of the b maXX 5500 and b maXX 6500 series are equipped with integrated DC link capacitors as standard, the two devices for two drives, for example, only need to be connected in the control cabinet with two cables.

What are the advantages of a DC link connection?

Energy exchange between drives: In a DC link system, drives that brake can feed energy back into the DC link. This braking energy can be used by other drives that are accelerating. This significantly improves the efficiency of the overall system, as less energy is drawn from the power supply, and less energy is wasted as heat.
Reduction in energy consumption: The external energy requirement can be reduced by reusing braking energy. This leads to lower operating costs and a better energy balance.
Hardware cost savings: Since brake resistors can be designed smaller or eliminated entirely, control cabinets can be made smaller. This reduces the cost of the required hardware.
Greater system availability: Thanks to energy buffers, the machine can often be shut down in a controlled manner in the event of a malfunction, meaning that it is ready for use again more quickly.
Lower network load: Energy exchange via the DC link reduces power supply demand.
Reduction of energy & costs as well as CO₂ footprint.