DC/DC converters in the industrial environment

Reading time – approx. 5 minutes – DC DC converters in the DC voltage network of industrial production offer a number of advantages. In this article, we would like to show you the reasons in favour of switching to direct current in an industrial environment.

At the end of the 19th century, Tesla, Westinghouse and Edison engaged in a so-called electricity war. Due to several decisive advantages, Tesla and Westinghouse were able to prevail in this conflict with alternating current technology, and a long-lasting era of this type of energy supply began. Now, almost 125 years later, the German Federal Ministry for Economic Affairs and Energy has been funding a cross-sector research project called “DC Industry” since July 1, 2016. The aim of this project is to convert the energy supply in industrial production to direct current using DC-DC voltage converters. Such a conversion affects not only the supply networks, but also the power electronics in industry to the same extent. The advantages and disadvantages of both types of supply and the resulting consequences for consumers are analyzed below.

Reasons for switching to DC-DC converters

When choosing a suitable power supply, a distinction must be made between two separate requirements. The energy transmission from the generator to the consumer and the functioning of the consumers. High voltages are required to be able to transport electricity over long distances with as little loss as possible. In the past, it was only possible to adjust the voltage economically with alternating voltage. However, transporting energy using alternating voltage leads to losses depending on the distance and the necessary insulation. These losses are due to the capacitive and inductive properties of the line, which lead to a constantly occurring reactive current depending on the AC frequency and the length of the line. Furthermore, as a result of the so-called skin effect, in which the charge carriers move more on the surface of the conductor due to the high frequency, thicker cables are required than for a comparable DC transmission in order to provide the current with a larger conductor surface.

The development of high-power thyristors and IGBTs (insulated gate bipolar transistors) has made it possible to convert high AC voltages to high DC voltages and back on a larger scale, thus enabling more efficient energy transmission via HVDC lines (high-voltage direct current transmission). A few years ago, the majority of consumers such as light bulbs, vacuum cleaners and various tools and machines drew their energy from alternating current. While resistive loads such as light bulbs or heaters can be operated with both types of current, motor types were developed early on that can generate mechanical energy directly from alternating current almost maintenance-free and without brushes, such as the asynchronous motor and the reluctance motor. Other motor types, such as the universal motor or single-phase series-wound motor, require brushes but work with both direct and alternating current.

This has changed and will change drastically with the current industrial revolution and advances in battery development. Whereas the overall efficiency of the supply of electrical energy used to be around 65%, current estimates suggest that it is now only around 56% due to the increased demand for DC voltage and the resulting need for conversion from AC voltage. If there is no rapid switch to direct current in the course of the decentralization of the energy supply in combination with the changed consumer requirements, the energy balance is likely to become significantly worse in the future.

DC/DC converters in the direct current supply

A high-voltage direct current supply offers the economically viable option of a redundantly secured decentralized energy supply in industry. The use of battery storage to buffer load peaks and to bridge grid failures reduces energy costs and the dimensioning of supply lines. This approach requires various DCDC converters for implementation. Powerful regulated DCDC converters with an integrated charge maintenance program are required to charge the batteries of the energy storage systems from the DC grid. By networking the power electronics involved, the charging process can be carried out with low-cost night-time electricity or at times of energy oversupply, which reduces the load on the energy infrastructure.

12 VDC is required to supply computers and servers as well as the low-voltage electrical systems of vehicles in automotive plants. These 12 VDC can be provided with high stability and accuracy by DCDC converters with a wide-range input, despite possible fluctuating HV battery voltages. Around 70% of industrial power consumption is used to supply electric motors. These drives are increasingly using frequency converters with their own DC link for speed control. By using a central DCDC converter, which supplies several frequency inverters with the necessary DC link voltage, the design of the frequency inverters can be significantly simplified. This not only reduces the acquisition costs, but also increases the efficiency of the system.

Conclusion

Whether direct current will completely replace alternating current in the future, or whether it makes sense for the two variants to coexist, can only be clarified once a number of technical and economic issues have been resolved. However, according to Gunther Koschnick, Managing Director of the ZVEI Automation Association, the elimination of many current transformers in drives, electronics and charging infrastructure could lead to energy savings of around 10%. At the same time, the supply networks can be made more stable and the devices more compact and fail-safe.