Do wireless BMS hold the key to the future of EVs?

The efficiency, longevity, and performance of an EV is clearly of paramount importance, and the BMS is an essential component in achieving this. Traditionally, every battery cell must be connected with wires to monitor and regulate energy and performance. However, we don’t tend to consider how all of that wiring and cabling hinders reliability, distance, maintenance, and overall costs.

So, what if that burden of weight on the BMS could be removed and the system could be operated wirelessly? TI’s new next-gen wireless BMS solution eliminates the need for bulky communications wiring, in turn creating new and easier design opportunities, and ultimately, improving drive range and reliability for EVs worldwide.

Wired vs wireless

A traditional BMS solution is wired. Today’s battery monitors are connected with a daisy chain communication interface. Functional safety is of major importance and safety requirements for a BMS are rigorous, and so need to be ASIL D compliant and support a single twisted pair interface. This can be connected in a ring architecture for reliable communication, even in the event of a cable break.

However, there is a downside. Every battery cell must be connected by cabling to a monitor, which regulates energy performance, and the heavy-duty copper wire, which is required to make the cabling more reliable, produces a bulky labyrinth of battery management cabling.

“This standard set-up requires a lot of complex wires, connectors, and isolation components, such as high voltage capacitors and transformers,” commented Karl-Heniz Steinmetz, General Manager for Worldwide Automotive Powertrain at TI. “On top of that, the wiring harness and connectors are quite a common source of cable failures, and it’s the number one reason for field returns. That makes warranty repairs, cable failures, and battery replacement super expensive.”

In comparison the TI solution for wireless battery management enables a reduced total cost of ownership of the complete battery in a hybrid electric vehicle or electric vehicle. Steinmetz added: “TI’s solution provides a direct cost reduction of the battery management system - reducing the complexity of the design by simplifying the wiring harness, removing cables, and the isolation connectors. In a wireless scenario you can establish a direct link from the battery management unit (BMU) to each wireless node, and that greatly improves the reliability of the complete system.”

Not only that, but a wireless BMS will also have an impact during an EV’s manufacture, by reducing assembly costs. The complex wiring from module to module is done manually today and involves working in a high voltage environment. “This is tricky and potentially dangerous, so by creating a wireless BMS these signal cables are removed, thus helping to reduce the manufacturing assembly cost,” Steinmetz continued.

A wireless BMS also enables easier maintenance and replacement of battery modules - instead of replacing the workings of the complete battery, with a wireless connection, you only have to disconnect the power lines – a far simpler task.

Finally, a wireless BMS also facilitates a second life business model for the battery. In a wireless battery management system, state of charge and state of health information is available on the module level, not only in the central system. 

“At end of life of the automotive use case this enables the battery to be sold into a second life application. In simple terms, that means you turn the cost centre into an asset. Instead of recycling a battery at the end of its life, you can take out the complete module and put it elsewhere in a second life use case, and this is why we believe the wireless battery management system will have a strong footprint in future electric and hybrid electric cars,” Steinmetz added.

The battery monitor

With the flexibility to scale designs across production models, automakers can advance to production faster with TI’s wireless BMS offering, including the SimpleLink 2.4-GHz CC2662R-Q1 wireless microcontroller (MCU) evaluation module, software and functional safety enablers such as a safety manual; failure mode and effects analysis (FMEA); and diagnostic analysis (FMEDA).

To speed automakers’ development time, TI requested that TÜV SÜD, the industry’s functional safety authority, independently evaluate the quantitative and qualitative error-detection performance of TI’s wireless BMS functional safety concept, as well as the feasibility for automakers to achieve Automotive Safety Integrity Level (ASIL) D, the highest level of International Organization for Standardization (ISO) 26262 certification.

Using a new wireless protocol, developed specifically for the wireless BMS use case, TI’s wireless BMS functional safety concept addresses communication error detection and security. The proprietary protocol via the CC2662R-Q1 wireless MCU enables a robust and scalable data exchange between a host system processor and the newly announced BQ79616-Q1 battery monitor and balancer.

“We have to remember that a BMS system needs to do two things perfectly – one is measure accurately and the second is transmit information reliably. Accuracy in measuring voltage, as well as temperature of the cells in the battery packs, remain paramount to guarantee the maximum mileage and maximum energy extracted between every recharge,” said Ivo Marocco, TI’s Director of Business Development and Functional Safety for Battery Automotive Products in HEV/EV.

“TI’s BQ79616-Q1 family plays a fundamental role in ensuring that, with the highest possible accuracy in measuring these parameters. At the same time, the functional safety aspects related to monitoring is becoming more and more relevant.”

As we see a proliferation in the automotive market heading towards electrification, and with more and more electronics within the car, having the highest possible level of safety is becoming a trend across the board and today ASIL D is what the OEMs and tier ones are requesting.

Marocco added: “This is understandable because they want to have the maximum possible coverage in detecting failures when they happen and in the fastest possible time - to report them to the brain of the system. Ensuring safety of passengers as well as damages to the vehicle itself, are the key factors that can be achieved with an ASIL D system - and the wireless BMS system from Texas Instruments is ready to do that.”

Connectivity

A wired BMS solution has several challenges associated with detecting failures, cost of repair, bulky cables and so on. Depending on the size of the battery the weight savings of a wireless BMS can be anywhere between 75lbs at the low end to about 150lbs to even 200lbs in some of the state-of-the-art battery packs that we have in today’s EVs - and that number is only going to increase.

However, add to that weight saving the advantages of cost of repair, speed of identifying faults and resolving them, and a wireless solution starts to look much more attractive. However, aligned to that is the network availability of a wireless system.

“The connectivity element is very crucial in a wireless BMS,” said Ram Vedantham, 2.4GHz Business Line Manager, Connectivity at TI, “to ensure that you can reliably send data from the battery controller unit to the cell supervision unit and vice-versa. In this respect, the fundamental role of connectivity is to make sure that the availability of data is ensured and that the latency as well as throughput guarantees are maintained.”

Rivalling wired connections, TI’s wireless protocol for BMS via the CC2662R-Q1 wireless MCU offers what TI claims is the industry’s highest network availability of greater than 99.999% and a network restart of 300ms maximum availability. With this wireless MCU, dedicated time slots that provide high throughput and low latency protect data from loss or corruption while enabling multiple battery cells to send voltage and temperature data to the main MCU with ±2-mV accuracy and a network packet error rate of less than 10^-7. 

Automakers can mitigate potential threats with security enablers from TI such as key exchange and refreshment; unique device authentication; debug security; software IP protection with a joint test action group (JTAG) lock; Advanced Encryption Standard (AES) 128-bit cryptographic acceleration and message integrity checks.

Vedantham added: “What is particularly unique about the TI wireless BMS solution is that we use three known proven techniques in terms of frequency: mitigating the interference coming from different sources; time division multiplexing, which makes sure that you are multiplexing across different nodes with minimum interference, and with guaranteed latency bound for each of the nodes; and reducing any kind of interframe spacing, or dead time, where you don’t transmit anything over the air. So we maximise the air time by packing data very efficiently.

“By using these three proven techniques, and by using a simple configuration where you can potentially support multiple star networks within the wireless BMS, we actually have a very simple solution which is unique to TI.”

Protocols

Using a new wireless protocol, developed specifically for the wireless BMS use case, TI’s wireless BMS functional safety concept addresses communication error detection and security. The proprietary protocol via the CC2662R-Q1 wireless MCU enables a robust and scalable data exchange between a host system processor and the new BQ79616-Q1 battery monitor and balancer.

“We have a proprietary interface mainly because we want to target latency throughput, as well as packet error rate requirements that are needed for this kind of system, to go along with the other benefits that wireless offers,” added Vedantham. “We are looking at how we can standardise this as part of a longer-term evolution - as more OEMs become engaged in this kind of approach - but at this point, a proprietary interface is necessary to make sure that we guarantee all of those requirements.”

TI has designed this proprietary protocol from scratch for use in the automotive use case where functional safety is of a major importance. “By combining ISO 26262 with an ASIL D level battery monitor, and a quality managed radio IC, and then putting that all together with the protocols specifically designed for the use case, that has allowed us to run a performance assessment of TI’s wireless BMS with TÜV SÜD,” added Steinmetz.

This enables TI to support the customer in the full package - not only the IC for the battery monitor or the radio, but the full proprietary protocol. Steinmetz continued: “As well as the concept report, including the failure mode diagnostic analysis, this is a big enabler and a huge step forward, compared to what is available in the market today, and I feel strongly that we can make the statement of being the most scalable BMS solution.”

TI claim that the deterministic protocol provides the highest throughput in the market, enabling automakers to create a battery module using a single wireless system-on-chip connected with multiple BQ79616-Q1 battery monitors for different configurations such as 32-, 48- and 60-cell systems.

The system is designed to support up to 100 nodes with low latency of less than 2ms per node and time-synchronised measurements across every node. The CC2662R-Q1 wireless MCU isolates individual cell monitoring units, eliminating the need for and cost of daisy-chain isolation components.

The BQ79616-Q1 battery monitor and balancer offers different channel options in the same package type, providing pin-to-pin compatibility and supporting 100% reuse of the established software and hardware across any platform.

Marocco added that the automotive market is heading in a direction where the OEMs will provide different types of car models, and this means different types of range. That translates into different sizes of batteries. This has prompted TI to ask the question of how to make its solution modular and scalable, as the size of the battery changes.

“The BQ79616 family can enable this by providing different types of solution and channel options in the same package type. The direction of the industry is keeping the overall cost contained, thus enabling a solution that offers an optimised choice, without wasting any channel or component that is not needed. So, having a solution that enables scalability, without paying for what you don't need, is a huge differentiator for TI.”

A next-gen solution

Vedantham continued: “We feel that our solution is the most advanced on the market from three perspectives - functional safety, performance and cost. We have what is the industry’s first and only ASIL D compliant system; our solution is scalable, and while we’re guaranteeing all of these performance benefits, we also take a lot of pride in the way we factor and develop these devices to be auto-quality compliant, and make sure that the cost points are very attractive for customers.”

Marocco added: “We have enabled the integration of a huge amount of discrete components inside the IC and innovation in terms of management, by adding a lot of intelligence inside the IC. We have also developed a set of diagnostic tools to enable the system to achieve maximum speed in detecting failure, without additional interaction from the ECU towards the monitor itself, and so in that, we think we have established ourselves at the top of the pack in the semiconductor industry.”

Steinmetz concluded: “TI are the first to achieve the wireless battery management safety concept, assessed by an independent party like TÜV SÜD and achieving ASIL D compliance. We’re able to support customers with a full system, not just pieces of it. We have really promising ongoing collaborative discussions with a number of leading OEMs and tier ones, and we have confidence that you will see our solutions in the market quite soon.”