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Resolving Controller Area Network communications problems in large-scale energy storage

By HMS Networks
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Battery storage is key to the transition away from fossil fuels to more sustainable, renewable energy-based energy systems, and in many ways communication networking is the key to better battery storage. Here, the team from HMS Networks discusses how it solved issues associated with Controller Area Network (CAN) communications for a customer in the energy storage space.

A battery energy storage system (BESS), usually based on electrochemistry, is designed to store electric charge by using specially developed batteries, so that the stored energy can be utilised later. Battery advances have now shaped BESS into a commercial reality.

While costs are still high compared to grid electricity, the cost of energy storage has been plummeting. There has been a 50% decrease in the cost of energy storage over the last two years. Many governments and utility regulators are actively encouraging the development of battery storage systems with financial incentives, which is likely to lead to further growth.

A BESS integrates a variety of disparate devices or subsystems within a single application – from batteries used in the automotive sector to air conditioning, ventilation and fire alarm systems from the building sector and controls from the industrial environment. These subsystems are networked together using a multitude of different protocols.

While these components and subsystems are often an ideal fit for the intended application, communicating with them can be challenging when the interface options are limited interface or non-existent. However, a majority of systems will offer at least a serial or CAN-based RS232/485 interface.

Because of their roots in the automotive segment, the battery packs utilised in BESS will often provide a CAN communication interface. CAN (Controller Area Network) is a bus-based system in which all nodes are connected in parallel to a bus consisting of two wires, terminated at both ends with a resistor.

CAN-based communications issues

During the early-stage commissioning of one such multi-megawatt BESS project, site technicians identified CAN-based communications issues at the battery rack level. This particular system networked multiple rack-level BMUs with a centralised “master” BMU utilising CAN in order to facilitate a cost-effective large-scale deployment.

In a CAN network, specific design and installation requirements must be met to maintain reliability and overall communication stability. These include the network length and topology, as well as the cabling itself and the terminations. Because it is necessary that an equal signal level is present at all nodes within a defined bit time, the total network length is limited.

The company contacted HMS Industrial Networks to request assistance to troubleshoot and resolve the issue and achieve communications stability. Under its Ixxat brand, HMS offers communication expertise for a wide range of users, including those in the energy and automotive industries. HMS was able to effectively analyse and troubleshoot the existing system remotely and recommend multiple approaches towards a resolution.

HMS’ experience in these situations combined with an extensive toolbox of diagnostic tools and topology components led to a successful resolution for the customer and a successful deployment of another large-scale BESS.

Ixxat provides a range of both standardised and customised software and hardware enable safe and reliable communications based on CAN, CAN FD and Industrial Ethernet, inside industrial automation devices, including battery storage systems, cars and medical equipment. The range includes gateways for smart grid energy systems.

HMS’ ixxat products for CAN-based networking and device protection. Image: HMS Networks.

Remote diagnosis utilising digital tools

In this application, HMS used digital tools to enable remote troubleshooting support to a site halfway around the globe. Specific CAN bus analysis tools included CANcheck and USB-to-CAN V2, combined with the CanAnalyzer software interface.

For error analysis, the distant customer carried out signal measurements on the bus and checked the wiring. Working jointly, systemic physical-layer problems were identified early. By analysing the CAN waveforms, it was shown that the network instability was due to excessive capacitive load combined with signal reflections.

Common contributors to such symptoms are

  • use of non-conformant cabling
  • cabling length being exceeded
  • lack of sufficient shielding/grounding.

The total physical cabling length of this system was roughly 115m. Whereas a 500 kbit CAN network typically can achieve lengths of 100-110m, the underlying issues on this system limited the length even more, before active error frames appeared.

In addition, system rewiring and cable replacement was not possible due to project requirements and physical limitations. The intuitive choice – implementing CAN repeaters to “extend” the network – was also inapplicable for this system: although CAN repeaters do provide bit-wise refreshing of signal levels, their signal propagation delay time effectively only adds length to a line topology network.

So, a different approach was needed!

Intelligent CAN bus segmentation

The HMS team proposed segmenting (sub-dividing) the overall network, using CAN topology components to improve the signal quality.

The larger CAN network was intelligently divided into multiple, shorter segments utilising two-channel CAN bridges, which offer more precise segmentation of the network, with two repeaters for signal refreshing. This allowed each sub-segment to maintain the intended baud rate along with the rest of the overall larger network. In addition, electrical disturbances are also not transmitted across the CAN bridge, further improving the overall signal quality on all segments.

“It just took a few weeks to complete the job from start to finish,” said Thomas Conz, Product Line Director at HMS Networks, based in Ravensburg, Germany.

“We applied our problem solving capabilities and took the customer step-by-step with us to solve the problem remotely. So it took us approximately two weeks to do the investigation phase with the customer, a week to send the device over and another week to check that the solution was working properly. Thereafter, the solution could be mass deployed and our customer was able to make the final buy-off of the system.”

Thomas Conz sees a lot of potential for BESS customers to improve their efficiency in developing, commissioning and deploying their BESS systems onsite. Secure connectivity between batteries and the cloud can help to develop new revenue streams for BESS, including fast-response communication with sources of renewable energy, such as wind turbines.

HMS’ Thomas Conz says the team was able to quickly resolve the customer’s issues. Image: HMS Networks.

Why you should choose HMS Networks as the reliable industrial connectivity solution provider for your BESS:

  • Identification of system weaknesses on physical layer with direct suggestions for improving communication reliability
  • Cost-optimisation of system design for future deployments
  • Comprehensive network health analysis by the HMS support team and subsequent application of the appropriate topology solutions enabled robust and reliable CAN BMS communication for the customer in their grid-scale BESS deployments
  • Clear understanding of when and how to apply various CAN bus topology solutions (repeaters, bridges, gateways)
  • Single partner for global support services, as well as extensive product portfolio

References

Deploying and commissioning reliable, large-scale CAN-based BMS networks
https://www.ixxat.com/docs/librariesprovider8/ixxat-case-studies/mmi219-en-resolving-bess-communication-problems.pdf

On-demand webinar: Solving intelligent networking and data communication challenges for Battery Energy Storage Systems
https://youtu.be/hso7rQK9lko

Network topologies and properties as well as networking strategies in BESS applications
Internal Ixxat document – https://www.ixxat.com/applications/battery-energy-storage/networking-and-topology

Measures to reduce EM interference and protection against overvoltage for CAN network components
Internal Ixxat document – https://www.ixxat.com/applications/battery-energy-storage/device-and-system-protection

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