Wired vs. Wireless Communications in EV Battery Management

EV BATTERY COMMUNICATIONS Wired vs. Wireless Communications in EV Battery Management

17.02.2021 From Nigel Charig

Related Vendors

Rogers Corporation

Schunk Sonosystems GmbH

Diotec Semiconductor AG

AIC Europe GmbH

Finepower GmbH

more less

Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) depend on large numbers of battery cells to provide high voltages for their electric motors – and these cells’ health must be continuously monitored to assure vehicle safety and reliability. This article compares the relative merits of using wired or wireless solutions for battery monitoring systems.

The batteries of HEVs and EVs must be continuously monitored to ensure vehicle safety and reliability. Learn about the benefits of using wired or wireless solutions for battery monitoring systems in the following article.
(Source: gemeinfrei / Pixabay)

As vehicle emission control legislation becomes tighter worldwide, the case for Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) becomes stronger. However, the EV market is still relatively new and faces some challenges before it becomes entirely dominant. Development is still ongoing to maximize vehicle operating range, duration, safety, and reliability while minimizing cost, size, and weight.

The automotive industry is suffering the consequences of the COVID-19 pandemic, as its demand for semiconductors cannot be met due to production disruptions. (gemeinfrei)

These factors relate in large part to the batteries used, which are most commonly lithium-ion (Li-ion) and lithium polymer types. Li-ion batteries in particular demand special attention because each cell’s characteristics change in a different way . Therefore, each cell must be managed individually to avoid complete discharge and the resulting power loss – and an automotive battery pack typically comprises a large number of cells, which can be distributed.

The EV’s AC motor may demand up to 800 V or more; this translates into potentially 100 or more Li-ion cells stacked together in series inside the vehicle chassis. These high-voltage packs are increasingly requiring more sophisticated technologies to report cell diagnostics for each cell in a safe, timely and reliable manner. One common design technique is to implement a distributed battery pack system, which supports high-cell-count packs by using multiple high-accuracy battery monitors.

The EV battery communications requirement

The battery monitors, which are mounted one on each cell, must connect with a central Battery Management Unit (BMU) to make up a distributed Battery Management System (BMS). Accordingly, the BMS can operate in real time to monitor the performance of each cell within the EV. This way, the BMS can ensure that all cells are operating correctly, while load sharing is properly balanced.

However, designers must decide on which type of communication channel to use: the monitors can be connected back to the BMU either with wires, or wirelessly. There are several design considerations which must be traded off to decide on the best option for any particular project. We can look a little more closely at both approaches to better understand their relative merits.

The growth of the power electronics market is dominated by three factors: Renewable energies around the world, the increasing use of power electronics for the production of electric vehicles and the growing use of power electronics in consumer electronics. (gemeinfrei)

In a wired system, the monitors are connected in a daisy chain of twisted-pair cabling, which carries cell temperature and voltage data back to the BMU. Current sensing on the power line is also used to calculate the battery pack’s state of charge and state of health. For extra reliability, a ring cable can be installed, which can transmit data in either direction in the event of a daisy chain cable break. The BMU in turn interfaces to the vehicle’s control unit through a Controller Area Network bus (CAN bus).

A high voltage battery pack has a large number of monitors, which all need to communicate back to the BMU quickly; these can all be connected to the daisy chain. The system will also include high-voltage relay controls to ensure safe disconnection of the high voltage when the vehicle is not in use.

The wired solution requires isolation components on either side of the daisy-chain cabling to ensure robust communications in electrically noisy environments, and to comply with strict automotive Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC) limits.

TI offers a solution for both wired and wireless architectures, comprising hardware and protocols. Wired interfaces are supported by their BQ796XX devices with an RX topology similar to RS-485 – but with added design mechanisms to attenuate high common-mode voltages caused by the noisy conditions typical in vehicle environments.

TI’s wireless solution is based on their CC2642R-Q1 devices and their associated proprietary wireless BMS protocol. This is based on Bluetooth Low Energy technology operating at 2.4 GHz. Its star network configuration supports up to 32 monitors per BMU, and provides high throughput, low-latency data transmission. It also features a functional safety-rated protocol.

The interface transmits Universal Asynchronous Receiver-Transmitter (UART) data from the battery monitors to the BMU. This design provides natural isolation between the distributed BMS components.

Wired or wireless - what are the factors?

It may appear that adding an extra device for wireless communications creates extra cost and complexity. However, eliminating the cabling and high-performance isolation components necessary for wired communications robustness provides significant cost, weight and space savings. The wireless solution decreases overall vehicle weight and complexity.

Subscribe to the newsletter now

Don't Miss out on Our Best Content

Business E-mail

Please enter a valid mailadress.

By clicking on „Subscribe to Newsletter“ I agree to the processing and use of my data according to the consent form (please expand for details) and accept the Terms of Use. For more information, please see our Privacy Policy.

Declaration of consent

It goes without saying that we treat your personal data responsibly. Where we collect personal data from you, we process the data in compliance with the relevant data protection regulations. More detailed information is available in our privacy policy.

Consent to the use of data for advertising purposes

I consent to the use of my email address to send editorial newsletters by Mesago Messe Frankfurt GmbH, Rotebühlstr. 83-85, 70178 Stuttgart, Germany including all of its affiliates within the meaning of Section 15 et seq. AktG (‘Mesago’). I have viewed lists of each group of affiliates here for the Mesago.
The content of the newsletter covers the products and services of all of the companies listed above including, for example, trade magazines and specialist books, events and exhibitions and event-related products and services, printed and digital media products and services such as additional (editorial) newsletters, competitions, lead campaigns, online and offline market research, technical web portals and e-learning courses. If my personal telephone number has also been collected, it may be used to send offers for the aforementioned products and services from the above companies, as well as for market research purposes.
If I wish to access protected content online on portals of Mesago including its affiliates within the meaning of Section 15 et seq. AktG, I must register with additional data in order to access that content. In return for this free access to editorial content, my data may be used in line with this declaration of consent for the purposes described herein.

Right to withdraw consent

I am aware that I can withdraw this consent at any time with future effect. My withdrawal of consent does not affect the lawfulness of processing performed based on my consent before its withdrawal. If I wish to withdraw my consent, I can send an email to Mesago at privacy@mesago.com. If I no longer wish to receive individual newsletters to which I have subscribed, I can also click on the unsubscribe link at the bottom of a newsletter. I can find more information on my right to withdraw, how to exercise this right and the consequences of my withdrawal in the Privacy policy Editorial newsletters section.

Also, while wiring is reliable, and meets functional safety standards, it can break over time – and if it does, it can be complex to repair. Nevertheless, this situation can be somewhat mitigated by using a ring architecture, which features built-in redundant cables in both directions. Although the wireless solution means no wires to maintain, the design must overcome harsh automotive radio-frequency environments and line-of-sight challenges.

Without cables and isolation components, the wireless solution has a smaller footprint; this improves design flexibility, and provides more location options within the vehicle. It is also easier to service.

This article looks at the geographic origins of the inventions and innovation related to battery technologies to identify the top innovation centers in the world and their technology specialization profiles. (gemeinfrei)

Additionally. the wireless solution can improve measurement performance, as its star network configuration naturally supports time-synchronized measurements. This can be further improved by adding more synchronized sensing capabilities. By contrast, in a wired system, time-synchronized voltage, temperature, and current measurements must travel the length of the daisy chain, causing delay between different monitor readings. However, a delayed measurement feature can improve performance.

Security is another important concern. A wired solution means contained and fully secure communications, while it is possible to breach poorly designed wireless systems that lack security protocols.

Conclusion

The above considerations show that adopting a wireless design for an EV battery management system can offer advantages over a wired solution – but only if the wireless design is built to overcome the electrical noise and security issues found within a vehicle environment.

(ID:47132198)