Controller Area Network (CAN) buses, originally used in the automotive sector, are known for their robustness. However, specific requirements must be met to maintain reliability and overall communication stability. These include specific demands for the network length and topology as well as the cabling and terminations.
HMS recently deployed a large-scale CAN-based battery management system (BMS) for a customer with unique requirements. The customer was designing and deploying modular, scalable battery energy storage systems (BESS) which utilised a high bitrate CAN bus in the battery management system BMS network architecture.
During the early-stage commissioning of a multi-MW project, site technicians identified battery rack communications issues. Initial attempts to identify the root cause were unsuccessful, whereupon the customer contacted HMS to request assistance troubleshooting and resolving the issue and achieving communications stability in their battery/BMS network.
Remote diagnosis in collaboration with technicians, utilising digital tools
HMS leveraged digital tools to overcome time zones and provide thorough, remote troubleshooting support to a jobsite halfway around the globe. Specific CAN bus analysis tools were utilised including Ixxat CANcheck and USB-to-CAN V2 combined with canAnalyser software interface.
For the error analysis, the customer carried out signal measurements on the bus and checked the wiring. Working jointly with the customer, 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:
(a) use of non-conformant cabling
(b) cabling length being exceeded
(c) lack of sufficient shielding/grounding
Unfortunately, system re-wiring and cable replacement were not possible due to project requirements and physical limitations. Instead, a different approach was needed.
Solution through intelligent CAN bus segmentation
The total physical cabling length of this system was roughly 115m. Whereas a 500 kbit CAN network can typically only achieve lengths of 100-110m, the underlying issues on this system limited the length even more, before active error frames appeared. The HMS team suggested segmenting (sub-dividing) the network accordingly using the appropriate CAN topology components to improve the signal quality.
The intuitive choice – implementing CAN repeaters to extend the network – was not applicable 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.
Instead, the larger CAN network was intelligently divided into multiple, shorter segments utilising two-channel CAN bridges, which offered message-wise ‘repeating’ across all channels. 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, which further improves the overall signal quality on all segments.
Through close collaboration with the customer, Ixxat by HMS was able to effectively analyze and troubleshoot the existing system remotely and recommend multiple paths toward a resolution. Ixxat’s experience in these situations combined with an extensive toolbox of diagnostic tools and topology components lead to a successful resolution for the customer and the successful deployment of another large-scale Battery Energy Storage System.
HMS’s Ixxat offers numerous benefits to customers, including:
- Fast and professional remote support with extensive network analysis from resident CAN experts
- Identification of system weaknesses on the physical layer with direct suggestions for improving communication reliability
- Cost-optimization of system design for future deployments.
- Clear understanding of when and how to apply various CAN bus topology solutions (repeaters, bridges, gateways)
- One partner for global support: services as well as an extensive product portfolio
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