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"Power supply" is one of those hidden topics. You know you need and want a "good" one, but you don't need to construct it because there are so many fantastic modules on the market. And if you need to construct it, you take one of these great manufacturer's design tools to get an instant well-proven result. Deep in your mind, you know that a well-designed power supply is the foundation of a high-quality product. When it comes to IIoT and 4.0, we are talking of millions of new, additional devices that all need power. Some of them even need to run wireless and are powered by energy harvesting. So high efficient power supplies and ultra-low power devices are common topics in IIoT. There is another aspect that has nothing to do with demands but with new applications and chances: Once power supplies themselves are cyber-physical systems, you can build a super-smart grid. It offers immense potential for digital services and energy saving. In this article, I want to show some of these benefits, specifically with a DC grid concept.
More than a century ago, people decided to use AC power for public electricity distribution. DC was reserved for device internal power supplies and batteries only. The reasons why Tesla triumphed over Edison were rooted in the technical limitations of that time: High voltages, up to 380 kV, are essential for long way energy transport and needed to be converted to lower household voltages by transformers. And it was much easier to generate AC electricity with fixed frequencies using generators. For many generations of engineers, the handling of high voltage DC became a long-forgotten art.
The DC vision
With renewable energy, modern power semiconductors, and inverters, high voltage DC technology is no longer a Sleeping Beauty. Some years ago, engineers began to study DC power supply possibilities for a complete industrial plant. They could easily show many advantages:
- Highly efficient integration of green energy (integration of renewable energy and energy storage)
- reduced connection load
- reduced energy consumption
- increased system availability
The research project "DC-Industrie" was started in 2019 by the ZVEI (Germany's Electrical Industry) and is funded by the German Federal Government. Two of the project's objectives are
- The safe and robust energy supply of production plants and
- Maximum use of decentralized, regenerative energy generation.
The project also wants to prove evidence in model plants and transfer centres.
The following pictures have been taken from the project's documents with courtesy of ZVEI and project members.
This picture shows the status quo: A typical industrial AC grid.
Elements of a factory's DC grid
A centralized bidirectional AC/DC converter supplies all load sectors of a production pant with DC power, rated typically at 650 V. Because no additional rectifying is required, the plant's overall energy efficiency is increased. With a modern plant being an energy prosumer, energy feedback into the AC grid is also possible.
Photovoltaic cells and other renewable energies can be integrated much more comfortably in such a DC grid because there is no need to synchronize with an AC grid. Additionally, the losses in power conversion are reduced.
Another core benefit is the easy integration of energy storage with reduced conversion losses. The stored energy increases production stability in cases of AC net faults. It is also a fantastic possibility to reduce peak power consumption.
Think of all the wasted energy we pump into power resistors to convert kinetic or elevation energy into heat when stopping robot movements or lowering a lift. With a DC grid, It is much easier to use this recuperative provided energy.
Each prosumer of such a DC grid is intelligent. The DC-Industrie project has developed a decentralized grid management concept that brings the full potential of power balancing and stability enhancement to many industrial applications. Each prosumer monitors the grid voltage and reacts to it according to a predefined non-linear characteristic curve. This method does not need additional communication.
But a central control with a communication network is also possible and enables even smarter process dependent load balancing.
Are there any results?
Since 2018, the project partners have been developing suitable components. They are currently running in a total of 4 demonstration facilities at Daimler, KHS, and Homag. Measurements and tests will be and have already been carried out to validate the system concept.
Homag, a world-leading manufacturer of solutions for the woodworking industry, could demonstrate a 25% power consumption reduction of the CNC drives of their machines when using a DC grid. They also reported a substantial reduction of copper (55%) for power lines. Due to the higher voltage and only three conductors, they could use 3 x 1.5 mm² instead of 4 x 2.5 mm² for their 7.5 kW drives.
Daimler has implemented a 2 MW DC grid in one of their plants. This plant also has a 5.7 mWp photovoltaic installation.
Preliminary evaluations have shown a 6 to 10% reduction in the AC grid's energy consumption. The peak load demand could be reduced to values down to 1/9. Copper-use in cables is lowered by 30 to 50% (there is no reactive power transported, just active power).
So where are the disadvantages?
Although standardization is on its way, there are currently not many components available. So we all have to wait and look forward to using this trendsetting technology. Meantime you can read more about it here.
And what's about DC power grids and IIoT?
While the DC Industrie project does not have IIoT in its focus, I can see the driving force of DC grids for IIoT. The easier it is to influence actual power consumptions and delivery from a prosumer, the smarter cloud control can be. Many services could be built around the smart balancing of loads, including completely new business models for the energy industry. You can partially see the potential when observing the "smart meter" and "smart grid" technology for buildings. Just imagine the possibilities when talking about the much higher energy demand for industrial plants. As soon as their energy consumption and production can be predicted and controlled in short periods, we will see new services mushroom.
Further articles in this series are available: