Direct current grids in an industrial environment

Whether an existing system is being converted (retrofit) or a new system is being implemented on the greenfield - everything starts with the consideration of which loads can and should be supplied directly with direct current, starting with the lighting, technical building equipment, photovoltaic systems and storage systems through to the production facilities. The technology selected for the energy storage solution and its installation location - centralized or decentralized - are also important. The basic considerations are concluded with the decision on charging stations for electric cars at the plant. "The design of a DC network is initially no different from the AC world," says Matthias Unruhe, Director Corporate Facility Management at Phoenix Contact.

Questions about the voltage range or the selection of components quickly arise during implementation. The Open DC Alliance (ODCA) has created a system concept for the industrial context that provides many answers. In addition, the companies Schaltbau and Phoenix Contact offer a broad portfolio of components that are suitable for use in the DC environment. Hurdles that seemed insurmountable a few years ago, such as the cost of power electronics, are now much lower. Thanks to the close cooperation between Phoenix Contact and Schaltbau, two DC production sites have already been realized: Schaltbau's NExT Factory in Velden and Phoenix Contact's Building 60 in Blomberg.

The introduction of direct current systems in production logistics and industry holds great potential for energy savings, especially for dynamic loads such as robots: peak power can be increased by up to 85% and energy efficiency by up to 20%. There is also good experience with large electric motors with frequency converters as well as with direct current sources (PV systems, battery storage), consumers, lighting systems and charging stations. However, the path from planning to implementation was not easy for the DC pioneers.

When planning for the Schaltbau NExT Factory began in 2019, there were hardly any suitable components and standards for the use of DC technology on the market. Grid operators also had little experience with DC systems and their integration into the public grid. The search for suitable planners and installers was difficult as there were only a few experts in this field. However, this situation has improved in recent years. Intensive research has also been carried out at a scientific level. Several pilot projects have tested the feasibility and efficiency of direct current solutions under real conditions. Phoenix Contact has had similar experiences. "Once the initial considerations had been completed, one question arose: Where do we get the components from?" reports Matthias Unruhe. The answer was provided by Phoenix Contact's broad portfolio, including power modules from the Trio HP product family for setting up DC networks or the VAL-MB DC overvoltage protection for the safe operation of DC applications. The company has also been involved in DC research for a long time. Key components such as the ELR HDC circuit breaker and the ArcZero DC connector were developed at an early stage and are now in use in Phoenix Contact's Building 60. Ultimately, the implementation of DC systems is less complex than initially assumed. "A lot has happened recently that makes it easier to put a DC project into practice," says DC grid expert Christoph Neulinger from Schaltbau.

The production building of the future

Building 60 fully exploits the potential of direct current. It is designed for maximum flexibility, efficiency and stability by linking the relevant sectors with each other using direct current. It also optimizes the entire energy chain of generation, distribution, storage and consumption, as these areas already largely operate on a direct current basis. In concrete terms, this means that the direct current grid is fed from the AC grid with an output of 700 kW. PV-connected DC/DC converters with a total output of 120 kW operate in parallel and feed directly into the DC bus. Two branches are used for direct connection to the production machines. The recuperation energy from robots and drives is used here. Charging points connected to the DC grid are located in the parking lot in front of the building. If there is excess energy in the DC grid despite these consumers, it is temporarily stored in the DC-coupled battery storage system or fed back into the public AC grid via the bidirectional AC/DC converters.

Load management at sector level and higher-level DC grid management are based on the PLCnext Engineer software platform. The ELR HDC is used wherever DC loads need to be switched safely. If there is a need to connect DC loads to each other in a pluggable manner, the company relies on the ArcZero DC connector. This enables arc-free plugging and unplugging under load. The energy flows are recorded in the entire DC network using EMpro DC energy meters.

The DC high-bay warehouse

The logistics sector is another industry in which DC technology can fully exploit its potential. With a capacity of 50,000 storage locations and 5,000 transport operations per day, Schaltbau's automated small parts warehouse (AKL) forms the backbone of logistics in the NExT Factory. The swarm robots (ARC) play a key role here. The peak power of the mini-load warehouse, including the ARC, of just 18 kW is significantly lower than the peak load of conventional alternatives, which often operate with around 120 kW AC. Industrial trucks are often only in use for part of the shift. However, with the DC grid charging concept, the times when the vehicle batteries are not in use can be used sensibly for targeted discharging and grid recovery in order to expand the in-house energy storage system. The energy available in the batteries can help to minimize power peaks in electricity consumption or increase the self-consumption rate of the PV system. Furthermore, the intelligent use of dynamic electricity prices opens up additional potential: In times of high energy prices, the stored energy can be used to supply the building. When prices are low, on the other hand, the batteries of the logistics fleet can be recharged in a targeted manner.

Experience simplifies implementation

Production facilities or real-life role models therefore show that it is possible to operate energy-efficient DC grids in industry. "Cooperation based on trust and an open exchange of ideas are essential in order to implement such projects," says Dr. Martin Wetter, Executive Vice President Innovation at Phoenix Contact and member of the ODCA board. "The cooperation and good complementarity of the two companies' products have led to success," adds Guido Bachmann from Schaltbau. Standardization is making great strides in the direction of direct current, and the necessary components are available. The design and scaling of projects is also more successful, as there is now good experience of how systems should be set up. Contacts from Schaltbau and Phoenix Contact help with the design, construction and selection of components. In addition, the ODCA provides a broad partner network for exchange.

M.Sc. Tobias Lüke, Project Manager, Business Unit Power Supplies, Business Area ICE at Phoenix Contact, and M.Sc. Andreas Forster, Project Manager DC-Grid & Energy Management System at Schaltbau

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