Automotive Battery Management System Using Bluetooth LE

Bluetooth wireless technology is now ubiquitous. It is widely adopted in a still growing number of devices in various market segments, including cellular, PC, home entertainment, smart home, wearable, healthcare, IoT and automotive. Bluetooth annual shipments are expected to exceed to 7.6 billion units by 2027 according to ABI Research. The automotive market follows a similar trend of growing adoption of Bluetooth in several applications including in-car entertainment, car access / digital key, tire monitoring, and more. ABI Research predicts that Bluetooth annual shipment in automotive will exceed 180 million units by 2027.

The Bluetooth SIG recently rolled out the version 5.4 of the Bluetooth Core specifications. This latest version introduces some exciting features that will unlock the potential of certain high-volume applications. Electronic Shelf Labels (ESL) is one such leading and widely discussed application. But another promising application that would benefit a lot from this new release is the Battery Management System (BMS) in Electric Vehicles (EV). Let’s see why.

What is Battery Management System (BMS)?

Thanks to the recent government regulations in many countries to reduce CO2 emissions to limit climate change, the number of electric cars shipping every year is expected to grow significantly. According to Bloomberg New Energy Finance, the global EV annual shipments should reach 30M units by 2030, and 60M units by 2040.

At the heart of an EV is the battery pack. The battery pack is a complex assembly of multiple modules each containing hundreds of battery cells. In total a battery pack may contain thousands of cells.

A BMS is the “brain” of an EV battery pack. It is a crucial component of an EV, responsible for ensuring the efficient and safe operation of the EV. Its performance significantly impacts the driving range and battery life of an EV. The primary purpose of a BMS is to manage the battery’s health, performance, and safety.

The following are the key features of a BMS in an EV:

1. Monitoring battery status: BMS continuously monitors the battery’s temperature, voltage, current, and other parameters. It alerts the driver in case of any anomalies, such as overheating or overcharging, and takes action to prevent potential hazards.
2. Balancing cells: BMS ensures the cells in the battery are balanced, meaning they all have the same state of charge. Unbalanced cells can lead to reduced performance, capacity, and lifespan of the battery.
3. Cell protection: BMS protects the cells from overcharging and discharging, which can damage the battery and reduce its lifespan. It also prevents over-heating and controls the charge and discharge rates to maintain the battery’s health.
4. State of Charge (SoC) estimation: BMS estimates the remaining charge in the battery to provide the driver with an accurate range estimation. It also helps in optimizing the battery’s usage and charging behavior.
5. Communication: BMS communicates with other systems in the vehicle, such as the motor controller and the central unit, to optimize the vehicle’s performance and safety.

What are the benefits of moving to wireless BMS?

Traditionally, BMS uses wired connections to communicate with other systems in the vehicle. The BMS monitors the battery cells by collecting various parameter data. All cells and modules in a battery pack are connected to the central BMS with many wires and connectors, adding significant weight and wiring design complexity. This significantly impacts the overall manufacturing and assembly cost of the BMS.

With the increasing complexity of the EVs and the need for higher efficiency, lower cost, more precise monitoring and control of the battery, wireless technology has become essential. This is why the automotive industry is in the process of moving to wireless BMS and thus removing all these wires will bring the following benefits:

1. Cost-effective: Wireless BMS reduces the overall cost of the system as it eliminates the need for complex wiring and connectors that can also be sources of failure. Maintenance and repair costs are therefore also significantly reduced.
2. Flexibility: Wireless BMS offers flexibility in terms of installation and placement. It eliminates the need for complex wiring and allows for easy installation and maintenance. Moreover, wireless BMS is more scalable and opens the possibility to offer various form factors with various number of battery modules to accommodate different EVs requirements, all with the same BMS solution.
3. Real-time monitoring: Wireless BMS enables real-time monitoring of the battery’s status and performance, providing more accurate and reliable data. This is achieved thanks to the fact that a wireless chip may also integrate MCU capability. Hence a significant part of the data processing can be moved “to the edge”, hence offloading the central processor and reducing the latency.
4. Increased safety: Wireless BMS provides increased safety by reducing the risk of wiring issues, such as shorts and ground faults. Reducing the latency of data processing and diagnostic also contributes to increased safety.
5. Longer range: the removal of wiring and connectors significantly reduces the size and weight of the BMS. Reducing weight leads to longer battery range. A smaller form factor leaves more space for something else in the car, or alternatively opens the possibility to add more battery modules, also contributing to longer battery life.

What are the advantages of Bluetooth 5.4 for BMS?

Several wireless solutions are considered for wireless BMS. Some of them are proprietary and tailored specifically for the wireless BMS use case. However, there are significant advantages in going with a standard solution like Bluetooth, and in particular supporting version 5.4 of the Bluetooth Core specifications. Here are the reasons why Bluetooth LE 5.4 is suitable for wireless BMS:

1. High throughput: Bluetooth offers more than one megabit per second data rate, while alternative proprietary solutions are often far below that rate. Bluetooth can therefore transfer more data in a shorter time, fulfilling the requirements of BMS as a significant amount of data needs to be transferred to the central processing unit, scaling with the number of battery modules. Higher data rate also means lower latency, which is critical for safety.
2. Synchronized low latency and reliable connectivity: Bluetooth technology provides reliable data transmission even in noisy environments. A Bluetooth based wireless BMS is composed of several battery modules communicating to the central unit. Today’s battery pack usually contains less than ten battery modules. But this number could increase to several tens in the future. Each module needs to report data to the central unit in an efficient and fast way. A damaged battery cell needs to be diagnosed in a fraction of a second to avoid dangerous consequences like overheating. In the traditional Bluetooth LE topology, a central device can communicate with many peripherals. But each peripheral needs to wait until it is polled by the central device before being able to send data. This may lead to latency not compatible with the wireless BMS requirements, particularly when the number of battery modules increases. Version 5.4 of the Bluetooth Core specifications introduced a new feature called Periodic Advertising with Response (PAwR) that solves this limitation. Thanks to this feature, a central device (the car central unit in this case) can send advertising packets at fixed interval that are received by all or a group of peripherals or observers (the battery modules). This is an improved version of broadcasting as each observer has the opportunity to reply back to the central device in a predefined response slot. Moreover, any of the 40 available radio channels may be used to exchange data over the air, which makes the communication more reliable and immune to potential interferers.
3. Secured connection: Bluetooth technology offers secure communication, thanks to encryption and authentication, preventing unauthorized access and ensuring the safety of the vehicle and its occupants. Until version 5.4 of the Bluetooth specification there was no way to encrypt broadcasting data. It is now possible thanks to the new Encrypted Advertising Data feature, which complements very well PAwR for more secure communication.
4. Low-power: Bluetooth LE is by nature a low power wireless communication protocol. Moreover, when using PAwR, the central unit periodically sends advertising packets and the observers listen only during these advertising events while they can go to sleep in between. They may send a response only when they are requested to do so. This is quite power efficient, particularly for battery powered devices such as EVs.

5. Low cost: Bluetooth LE chips from major vendors are shipping in very high volume in various applications, leading to low selling price thanks to economy of scale and highly amortized development cost. They are cheaper than proprietary wireless chips which have been designed specifically for wireless BMS, hence shipping in lower volume with limited economy of scale.
6. Multi-source: the benefits of using Bluetooth LE are that chips from several vendors can be used in the supply chain. This allows BMS and EVs makers to have a second source in order to secure volume production and maintain price pressure.

Conclusion

BMS is a critical component in the automotive industry, responsible for ensuring the efficient and safe operation of EVs. Wireless BMS is lighter and more flexible than the wired alternative and is increasingly being adopted as battery pack complexities and form factors evolve. Bluetooth technology, in particular Bluetooth LE 5.4 with PaWR, is ideal for wireless BMS due to its very low-power consumption and reduced latency, coupled with the supply chain benefits arising from its standard, mass-deployed nature. As EVs become more prevalent, Wireless BMS based on Bluetooth will play a vital role in ensuring the optimal performance and safety of these vehicles.

CEVA is the leading provider of Bluetooth platform IP solutions for integration into SoCs, powering billions of Bluetooth-enabled devices to date in various market segments including IoT, wearable, hearable, smart home, mobile, industrial, and automotive. CEVA offers both Bluetooth LE and Dual Mode IP platforms, including baseband controller, radio and full software protocol stack, along with a comprehensive list of profiles to address a wealth of applications.

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