More efficient and more powerful with a DC link connection
A powerful way to improve the energy efficiency of electric machines is the smart use of braking energy. Baumüller connects its b maXX servo drives via a common DC link. In this way, the drive expert harnesses braking energy, makes systems more cost-effective, and can even increase the performance of electric drives.
What is a DC link connection?
A DC link distributes power within a single converter. A DC link connection is defined as a configuration in which multiple drives share a common DC link. The DC link connection can also serve as a storage medium for electrical energy. It can supply electrical energy, store it, or swap it between multiple drives. This allows the DC link connection to store braking energy and put it to other uses, such as smoothing out power spikes.
A DC link connection is a configuration in which multiple drives are connected to a single common DC link.
When does a DC link connection make sense?
Applications that consume a great deal of energy—such as those with multiple drives or machines that experience high power peaks—benefit from a DC link connection. In addition, machines that generate a lot of braking energy.
The DC link connection can be used to overcome various challenges:
- High energy consumption
- Cost pressure
- High performance requirements
What are the advantages of systems with a DC link connection?
Reduced energy consumption
A key advantage of the DC link connection is the more efficient use of energy through the storage and recovery of braking energy.
Here’s how energy recovery works: During normal operation, electricity powers the electric motor. In regenerative braking, this principle is reversed: when a motor decelerates, the system’s inertia generates kinetic energy. The motor now operates as a generator, which means that the magnetic field inside the motor induces a current in the coils. This converts mechanical motion into electrical energy. This energy can be stored in the DC link connection and distributed to other axes or fed back into the power supply. Without a DC link, this energy is lost as heat.
Reduced load on the power supply
The energy exchange within the system reduces the load on the power supply and improves the supply quality.
Without a DC link connection, each axis draws the required current from the power supply individually. When multiple drives accelerate at the same time, load spikes occur. In systems capable of feeding power back into the power supply, the impact on the power supply often fluctuates significantly. With a DC link connection, energy is distributed throughout the system. This stabilizes the power supply load; in other words, short-term fluctuations and peaks are not directly transmitted to the power supply but are buffered by the DC link. This also results in lower connected power and, consequently, lower life-cycle costs for the operator.
Cost savings
Systems with a DC link connection allow for lower initial costs.
In a DC link connection, multiple axes share a single power supply module, which helps reduce hardware costs. Less energy is lost as heat, so the cooling units can be smaller. In addition, the control cabinets are smaller, and there is no need to set up an independent power supply, since in the event of a failure, the stored energy is available to ensure a controlled shutdown. Regenerative energy can be utilized by other axes within the DC link connection; consequently, less energy is fed back into the power supply, making it possible to eliminate the need for power feedback units.
Higher performance
The DC link connection with an active mains rectifier unit allows the motor to operate over a wider speed range.
Active mains rectifier units decouple the machine from the power supply and increase the voltage from 540 V to 760 V. The higher voltage expands the motor’s speed range and increases the available power. This makes it possible to speed up processes or design smaller drives. This reduces investment costs and improves performance.
The various drive architectures with a DC link connection
Systems with a DC link connection can be implemented using various hardware components. Each topology meets different specific requirements and offers its own advantages.
Modular technology
A single power supply shares a DC link with multiple axes. The devices are connected via the Drive-Connect system; no additional wiring is required.
The devices: b maXX 5000 power supply units, b maXX 5300 axis modules, b maXX 6300 axis modules
Ideal for: applications where small- to medium-sized drives and more than three axes are used and only little braking energy is generated.
Why we do this: this drive topology is compact and particularly energy-efficient, and requires less wiring effort than a solution using standalone devices.
Example application
Lässer AG’s MVD75 high-performance shuttle embroidery machine:
Precision, dynamics, and reliability were the top priorities for Lässer AG’s embroidery machine. With over 700 stitches per minute, the MVD75 embellishes all kinds of textiles 24/7.
Baumüller’s highly dynamic DSD2 series servomotors meet the stringent requirements for acceleration ability and start-stop capabilities and feature an excellent torque-to-inertia ratio. This ensures maximum dynamics, i.e., fast and precise production of embroidery. The DSD2 drives are synchronized with high precision and, when used in conjunction with Baumüller’s stackable b maXX servo controllers, enable high positional and speed accuracy for maximum quality. The axes are connected to the power supply unit in the DC link, enabling them to operate with exceptional energy efficiency. The additional DC link capacitance unit temporarily stores energy during the braking process of the servo motors. The embroidery machine uses this for re-acceleration, thereby saving energy. The servo controllers are particularly compact, taking up minimal space in the control cabinet and requiring minimal wiring effort.
Active mains rectifier units
Multiple axes connected to the active mains rectifier unit via the DC link. The devices are connected via the Drive-Connect system; no additional wiring is required.
The devices: b maXX 5100 rectifier and regenerative feedback units, b maXX 5300 axis modules, b maXX 6300 axis modules
Ideal for: applications where generator-based energy is generated in the low- to medium-power range and needs to be fed back into the power supply.
Why we do this: it improves energy efficiency, and the active mains rectifier unit increases the voltage in the DC link, thereby expanding the motor’s speed range.
Example application
Handling unit for removing components from an injection molding machine
The biggest challenge in implementing the extraction unit was the system’s high dynamics and reliability. Even in the event of a power supply failure, all parts must be safely removed from the system to prevent damage to the injection molding unit.
Due to the high dynamic response, a great deal of kinetic energy is generated when the handling axes decelerate. This energy can be used by the axes during the injection molding process or fed back into the power supply. In the event of a power supply failure, there is always enough energy available in the DC link connection to ensure controlled deceleration and clearing of the machine. The use of an active mains rectifier unit — which regulates the DC link voltage — improved the control accuracy of the motor speed, a major advantage for this highly dynamic application involving varying load masses.
Standalone unit with modular technology
Standalone units with multiple axis modules and no separate power supply module.
The devices: b maXX 5500 standalone units, b maXX 6500 standalone units, b maXX 5300 axis units, b maXX 6300 axis units
Ideal for: applications where one large and several small drives are in use. Often also used for serial movements.
Why we do this: with this solution, we can apply the principle of modular design even to high-power applications, thereby offering a cost-effective and energy-efficient drive system.
Example application
Uniloy URH reciprocating blow molding machine:
As part of its ongoing effort to electrify its blow molding machines, Uniloy has entered into a partnership with Baumüller. The URH blow molding machine was implemented using DSD2 servo motors, DST3 torque motors, and servo drives from the b maXX 5000 series. In this configuration, b maXX 5500 standalone units are operated in a DC link connection with b maXX 5300 axis units. The drive that supplies the plasticizing unit also powers the two injection axes via the common DC link. This means that no separate power supply is required for the injection process, which saves costs and allows the drive system to be flexibly expanded to include additional axes. This results in a cost-effective, energy-efficient, and space-saving system.
Standalone units
Several standalone units connected via a DC link.
The devices: b maXX 5500 standalone devices, b maXX 6500 standalone devices
Ideal for: applications where two or more axes are to be operated in the high-power range.
Why we do this: the benefits of energy sharing come into play here as well.
Option: The b maXX 6500 standalone units are also available without a power supply. They then serve as axis units for high power outputs. If the power supply capacity of a standalone unit is sufficient, the remaining units can be implemented more cost-effectively without a power supply and can be powered via the DC link connection.
Active mains rectifier units with axis units for high power output
An active mains rectifier unit with one or more axis units connected to the DC link for high power output. Axis units for high power outputs are standalone devices without their own power supply.
The devices: b maXX 5100 rectifier and regenerative feedback units, b maXX 5500 standalone devices, b maXX 6500 standalone devices
Ideal for: applications requiring high power output and where large amounts of generator-based energy need to be stored or fed back into the grid.
Why we do this: energy needs to be fed back into the power supply at high power levels. The advantages of the higher DC link voltage can be utilized.
Example application
Servo-spindle press for metalworking manufactured by synchropress
Highly synchronized drive system for servo-spindle presses featuring b maXX servo drives, DSD2 servo motors, and DST2 torque motors.
Advantages:
- Supply-side decoupling via higher DC link voltage enables storing larger amounts of energy in DC link capacitors
- Higher DC link voltage extends the speed range of the motors
- Use of an active mains rectifier unit enables the regeneration of energy back into the power supply
Write us a message, our sales experts will be happy to advise you.
FAQ
Frequently Asked Questions About Baumüller’s DC Link Connection
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What is a DC link connection?
Motors and converters share a common DC link within the DC link connection. This means that the motor is not directly connected to the power supply. The converter is located between the motor and the power supply. If additional drives are connected to this DC link, this is referred to as a DC link connection. The DC link connection can include two or more drives. Energy can be stored, buffered, and distributed in the DC link. This enables energy sharing—that is, the efficient distribution of energy among multiple drive systems.
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When can a DC link connection offer advantages?
A DC link connection is particularly useful when a significant amount of braking energy is generated in the system. This braking energy can be used within the DC link connection to power additional axes.
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Why does an architecture with an active mains rectifier unit increase the motor’s speed range?
The active mains rectifier unit decouples the DC link from the power supply. This allows the voltage in the DC link to be increased from 540 V to 760 V. The motor can continue to operate above its nominal speed before field weakening begins. This increases the motor’s speed range.
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What does “modular technology” mean?
Baumüller uses the term “modular technology” to describe the combination of a rectifier or rectifier and regenerative feedback unit with multiple axes, connected via the Drive Connect System. The Drive Connect System is a connection method for the b maXX 5300 and b maXX 6300 axis units. It allows for the quick and easy combination of axis and power supply units via a rail and significantly reduces the amount of wiring effort required.
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Why does a DC link connection with an active mains rectifier unit reduce reactive power?
A DC link connection with an active mains rectifier unit reduces reactive power because the use of the active mains rectifier unit decouples the DC link from the power supply. This ensures that electricity is drawn from the power supply in a controlled manner. As a result, the current flows smoothly rather than in pulses; the voltage and current vary at nearly the same rate, and the power factor approaches 1. This means that almost only active power—and very little reactive power—is drawn from the power supply.
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Which devices can be connected in a DC link connection?
All devices in the b maXX 5000 and b maXX 6000 families can be connected to a DC link connection.
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Does a DC link connection also have disadvantages?
If careful consideration is given to whether the advantages of the DC link connection are realized in the specific application, there are no significant disadvantages.
