The background to the research project, which has been running since July 2016, is that direct current is seen as a key future technology for integrating renewable energy sources into production, which means that complex energy conversions - as are inevitably required with today's AC grids - can be avoided. A further benefit of 'DC industry' in industry is seen, among other things, in the energy network between the connected devices, because energy generated during braking can be fed back into the grid. This is not a new topic for Danfoss: the Danish drive technology manufacturer has already had a range of products or systems for DC networks with a connected DC link on the market for some time - for use in electrical DC networks on board ships, for example. The corresponding modular product system is based on the Vacon inverter family and ranges from the motor/generator application to the 'DC Guard' as an extremely fast shutdown device.

In addition, Danfoss is now launching two further drive approaches with servo and geared motors, which also already implement the basic approach of 'DC Industry'. The first is FlexMotion - a concept for linking servo drives together. It consists of the central MSD supply unit, which converts the alternating current into direct current, and the ISD 510 (integrated) or DSD 510 (decentralized) servo drives. The second is FlexConcept Advanced - a solution that uses DC coupling (load sharing) to enable a DC network with intelligent geared motors for a wide range of applications. "Last year, the kits were still a concept, but today they are a reality and will be available from mid-2019," says Per Boysen, Director Product Development Servo Drives at Danfoss Drives in Bruchsal.

According to Boysen, the systems mentioned are classified by the DC industry project as 'basic network without higher-level network management'. Nevertheless, these drive solutions already implement the basic approach of DC Industry with their continuous DC voltage supply without significant transmission losses and energy exchange between the connected motors.

The advantages for mechanical engineering

When asked what advantages DC technology can offer specifically for mechanical and plant engineering, Boysen replies: "Among other things, the installation effort is significantly reduced. As the central control cabinets with their inverters and cabling up to the motor are no longer required and only very small power cabinets with PLC, main distribution board, back-up fuses and mains chokes are needed at the application, control rooms are much smaller." In addition, energy consumption can be permanently reduced by using DC technology in suitable applications with many parallel braking and acceleration cycles. Boysen explains: "Operating several drives in a DC-Link network allows perfect load sharing. Here, motorized drives use the regenerative energy supplied by braking motors, which makes the system very efficient. In principle, only the differential energy for the process needs to be fed in thanks to the energy actively exchanged between the regenerative and motorized motors."

As far as implementation is concerned, the topic of 'DC Industry' is still in its infancy, but regardless of this, the following can be said: "VLT FlexMotion or FlexConcept Advanced can also be used relatively easily as an isolated solution within a classically installed factory system and the user can therefore set up a machine suitable for this solution today as described without having to convert their entire system to DC technology."