The shift towards electrification, especially with electric vehicles, means battery monitoring is going to be critical for safety and lifetime performance. Hoping to disrupt the battery management system (BMS) market, U.K. headquartered Dukosi has developed a wireless BMS that puts a chip and embedded software on every battery cell to eliminate masses of wiring harnesses and put intelligence into the battery itself.
We spoke to Joel Sylvester, founder and chief technology officer of Dukosi, to explain how the company’s solution is different to wireless BMS solutions already on the market, and what it means for the battery industry.
He said, “What we’ve developed is a cell monitoring device for use in very large high voltage lithium-ion battery packs, of the sort that you’ll find in electric vehicles, electric buses, marine applications, grid energy storage applications. Basically, anything that requires a large battery pack these days is moving to or has moved to lithium-ion chemistries and you need to monitor those cells very closely. There’s a lot of energy in them. You need to pay very close attention to what the cell voltage is, what the temperature is and so on in order to keep the pack safe and to make them last as long as you possibly can.”
“What we’ve developed is a silicon chip and the software to go with it that allows you to monitor the voltage, the currents, the temperature, and many other things characteristics of individual lithium-ion cells.”
So how is Dukosi being disruptive? He said, “What’s disruptive is when you put the chip onto the cell. Now you’ve got an intelligent cell that you can configure into battery packs of any size, shape, configuration. You can create multiple battery products using the same cells in the same intelligent cells. That’s more disruptive because it changes the way in which the battery industry is going to approach the way that they monitor and manage their batteries.”
He said that when talking to prospective customers the thing that always comes up first is about getting rid of wiring harnesses. “The pack manufacturers hate them. All they do is reduce the reliability, create safety issues, they’re expensive to design and manufacture and install, so getting rid of wiring harnesses is always the first one; after that, it’s the quality of the measurements. We can make a temperature measurement on every cell in exactly the same manner, position on every cell. That allows them to improve the performance of their battery packs.”
The need for battery management
It is accepted that battery monitoring is vital for safety and best lifetime performance, particularly in EVs, but current monitoring methods are an evolution from cumbersome old techniques, according to Dukosi. The company said a new, truly wireless approach can also leverage the advantages of fast and flexible edge computing.
The prime function of a BMS is to maintain safe charge and discharge, reducing risk of cell degradation, damage and even fire. The benefits go beyond that though, accurately knowing the state-of-charge (SoC) of a battery pack enables the vehicle range to be determined, reducing ‘range anxiety’ and charge times to be reduced.
Additionally, accumulation of monitored information such as temperature, voltage and charge/discharge cycles over time can indicate battery state-of-health (SoH). As a fleet of EVs ages, SoH of the battery can become a deal-breaker for ‘second life’ use, either in resale of the car, or re-purposing of the battery pack in another less onerous application such as grid energy storage. Maximizing battery longevity reduces the lifetime cost of the battery, and minimizes the frequency and cost of recycling, reducing environmental impact of transport generally.
Cables are a problem
Battery monitoring has been recognized for decades in industry and telecoms, where backup for critical systems is important. A 48V lead-acid battery array feeding a UPS in a server farm can afford wiring harnesses connecting the bulky centralized monitoring hardware to each cell, but carrying the principles over to EVs with up to 800V strings of cells in a highly contained and harsh environment is not an ideal solution.
However, that’s exactly how a BMS is currently typically implemented, and because of the high voltages and risk of wire abrasion with vibration, the cable connections to cells in strings have to be oversized for the signals they are carrying, with the associated weight and space penalties, not to mention installation costs.
‘Wireless’ battery monitoring for EVs would then seem an obvious solution to address this challenge. Solutions exist which have evolved from older modular architectures, where the voltages of a number of cells in a string are monitored. The resulting analog values are multiplexed in one of a number of modules built-in to the battery pack, ‘digitized’ and then passed over an RF link to a central processor.
The number of cells monitored is typically 12 or 14, limited by the voltage rating of the multiplexer, with each cell adding around 3.7V. The number of cells monitored is set to increase to 16 or higher, to reduce the number of multiplexers needed, but this only amplifies the need to use a high voltage technology in the IC fabrication process. This precludes the easy incorporation of local data aggregation and processing which therefore must be done centrally, creating a bottleneck in the RF connection.
More significant disadvantages though are that measurement accuracy of each multiplexed cell voltage degrades up the string and longer physical wire connections to each cell are needed. Noise pick-up is an additional concern. Close attention has to be made to the location of RF antennas, to ensure every module has ‘line-of-sight’ to the central receiver, or complex and unpredictable mesh networks have to be built, making data rates and latency unpredictable.
Enter ‘edge’ computing for batteries
Dukosi has hence adopted the idea of ‘edge’ computing – monitoring cells individually with local processing to interpret readings and wirelessly transmit instantaneous and aggregated data over time in the form of histograms created by proprietary embedded software.
The company said its ultra-low power hardware is a tiny CMOS chip powered by the monitored battery cell, so the IC technology is compatible with common processor cores and memory. No analog signal multiplexing is necessary, so precision is optimized and the chip is fitted directly at the cell for maximum measurement accuracy of both voltage and local temperature.
The problem of connection to an antenna is solved by the use of patented NFC technology. Similar to the inductive loops for ‘contactless’ payment, a thin, low voltage, single wire loop is routed around the battery pack, close to each Dukosi monitor, loosely coupling into a loop on the sensor with a few millimeters of physical separation. This ensures a fast and robust data connection but is enough to easily provide the electrical isolation needed for the highest battery pack voltage. Each IC has a unique identifier and is polled via the NFC connection by a radio manager which controls the communication process and passes data to the vehicle management electronics. The whole system is designed to be safe, as an ASIL C component of an ASIL D-rated battery pack.
Putting intelligence which is ‘always-on’ at the battery pack, even when the EV is not in use, opens opportunities for long-term logging of usage and performance data which can be interpreted as state-of-health and even maintained as provenance of the battery at any point in its life. With reduced hardware, cabling and installation costs, the lifetime benefit of such a system can be useful across all electric vehicle types, as well as in wider energy storage applications.
Sylvester explained how Dukosi is doing the wireless BMS differently. He said, “You need to make measurements on lithium-ion cells. But the devices currently on the market from some of the big-name semiconductor companies look almost exactly the same to those that were available in the late 1990s. It’s not really evolved very much in that time. The way that the technology has gone elsewhere is trying to address more and more cells at the same time, so 12 cell, 14 cells, 16 cells and that’s taking them down a particular route of trying to go to higher and higher voltages.”
“Our product just does one cell at a time, so you need a lot more of them. But it makes the measurements on that cell really well: we’ve got industry-leading accuracy on the measurements. We can measure temperature on every cell. We can run algorithms on the cells to tell you what the state of charge is or the state of health, or many other characteristics of the lithium-ion cells, we can do that really, really well at one cell and then you can connect them all together very easily into a battery network. No additional connectors. No wiring harnesses or all of the other stuff there. That’s all gone.”
“That battery network then tells you everything you need to know about the battery system. You’re taking away cables, you’re taking away connectors, you’re taking away all the mechanical structures you require to support them and make sure they don’t kind of braid, moving the measurements, the sensor, right to the point where you need to make the measurements.”
You’ll be able to hear the full interview with Joel Sylvester on the embedded edge with Nitin podcast.
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