What is a Battery Management System (BMS)? What are the benefits of a Bluetooth Low Energy automotive battery management system?

Today, Bluetooth wireless technology is ubiquitous and is widely used in a variety of devices, with market segments covering cellular, PC, home entertainment, smart home, wearable devices, healthcare, IoT and automotive, and the number of devices using it is still on the rise.

According to statistics from ABI Research, annual shipments of Bluetooth devices are expected to exceed 7.6 billion by 2027. The automotive market is showing a similar trend, with Bluetooth being increasingly adopted in a variety of applications such as car entertainment, car access/digital keys, tire monitoring, etc. ABI Research predicts that annual shipments of automotive Bluetooth devices will exceed 180 million by 2027.

The Bluetooth SIG recently released version 5.4 of the Bluetooth Core Specification. This latest version introduces some exciting features that will unlock the potential of some high-volume applications. Electronic Shelf Labels (ESL) is a leading and widely discussed application. And another application that is expected to benefit greatly from this new version is the Battery Management System (BMS) for Electric Vehicles (EV). Let’s take a look.

What is a Battery Management System (BMS)?

As many governments have recently introduced regulations to reduce carbon dioxide emissions to limit climate change, annual electric vehicle shipments are expected to grow significantly. According to Bloomberg New Energy Finance, by 2030, global annual electric vehicle shipments will reach 30 million, and by 2040, they will reach 60 million.

The battery pack is the heart of an electric vehicle. A battery pack is a complex assembly consisting of multiple modules, each containing hundreds of battery cells. A battery pack may contain thousands of battery cells in total.

BMS is the "brain" of the electric vehicle battery pack and a key component of the electric vehicle, responsible for ensuring that the electric vehicle operates efficiently and safely. Its performance significantly affects the driving range and battery life of the electric vehicle. The main purpose of BMS is to manage the health, performance and safety of the battery.

The following are the main functions of an electric vehicle BMS:

1

//Monitor battery status

The BMS continuously monitors the battery's temperature, voltage, current and other parameters. If any abnormality occurs (such as overheating or overcharging), the BMS will alert the driver and take measures to prevent potential danger.

2

//Balance the battery cells

The BMS ensures that the battery cells in the battery are balanced, that is, the state of charge of the battery cells is the same. Unbalanced battery cells will lead to reduced performance, capacity and service life of the battery.

3

//Battery cell protection

The BMS prevents battery cells from overcharging and overdischarging, which can damage the battery and shorten its life. It also prevents overheating and controls the charge and discharge rates to maintain the health of the battery.

4

//State of Charge (SoC) estimation

The BMS estimates the remaining charge in the battery in order to provide the driver with an accurate range estimate while helping to optimize battery usage and charging behavior.

5

//Communication

The BMS communicates with other systems in the vehicle, such as motor controllers and central units, to optimize the performance and safety of the vehicle.

What are the benefits of migrating to a wireless BMS?

Typically, the BMS uses wired connections to communicate with other systems in the vehicle. The BMS monitors the battery cells by collecting data on various parameters. All battery cells and modules in the battery pack are connected to the central BMS through a variety of wires and connectors, which significantly increases the weight and wiring design complexity. This significantly affects the overall manufacturing and assembly costs of the BMS.

As electric vehicles become more complex and require increased efficiency, lower costs and more accurate battery monitoring and control, wireless technology becomes essential. That’s why the automotive industry is turning to wireless BMS. Removing all those wires will bring the following benefits:

1

//Economical and practical

Wireless BMS reduces the overall cost of the system because there is no need for complex wiring and connectors, which can be a source of failure. Therefore, maintenance and repair costs are also significantly reduced.

2

//flexibility

Wireless BMS is flexible in installation and placement. There is no complicated wiring, which is easy to install and maintain. In addition, wireless BMS is more scalable and available in various form factors, with different numbers of battery modules to meet different electric vehicle needs, all of which can be achieved with the same BMS solution.

3

//Real-time monitoring

Wireless BMS can monitor the status and performance of the battery in real time, providing more accurate and reliable data. This is because the wireless chip can also integrate MCU functions. Therefore, most data processing tasks can be "migrated to the edge", thereby reducing the burden on the central processor and reducing latency.

4

// Improve security

Wireless BMS improves safety by reducing the risk of wiring problems such as short circuits and ground faults. Reducing data processing and diagnostic latency also helps improve safety.

5

//Longer driving range

Removing wiring and connectors can significantly reduce the size and weight of the BMS. The reduced weight will extend the battery's range. The smaller size can free up more space for other items in the car, or allow for the addition of more battery modules, which also helps extend the battery life.

What are the advantages of Bluetooth 5.4 for BMS?

There are a variety of wireless solutions considered for wireless BMS. Some of them are proprietary and tailored for wireless BMS use cases. However, using a standard solution such as Bluetooth, especially supporting Bluetooth core specification version 5.4, has significant advantages. Here are the reasons why Bluetooth LE 5.4 is suitable for wireless BMS:

1

//High throughput

Bluetooth can provide data rates of more than 1 megabit per second, while other proprietary solutions are usually much lower than this level. Therefore, Bluetooth can transmit more data in a shorter time, meeting the requirements of BMS to transmit large amounts of data to the central processing unit and scale with the increase in the number of battery modules. Higher data rates also mean lower latency, which is critical for safety.

2

//Synchronous low latency and reliable connection

Bluetooth technology provides reliable data transmission even in noisy environments. A Bluetooth-based wireless BMS consists of multiple battery modules that communicate with a central unit. Currently, a battery pack typically contains less than ten battery modules. But this may increase to dozens in the future. Each module needs to report data to the central unit efficiently and quickly. A damaged battery cell needs to be diagnosed in a split second to avoid dangerous consequences such as overheating.

In the traditional Bluetooth LE topology, a central device can communicate with many peripheral devices. However, each peripheral device needs to wait until it receives a poll from the central device before sending data. This can cause latency that does not meet wireless BMS requirements, especially when the number of battery modules increases.

Version 5.4 of the Bluetooth Core Specification introduces a new feature called Periodic Advertising with Response (PAwR) that addresses this limitation. With this feature, a central device (in this case, a car central unit) can send advertising packets at fixed intervals, which are received by all or a group of peripheral devices or observers (battery modules). This is an improved version of advertising, where each observer can reply to the central device at a predefined response time. In addition, any of the 40 available radio channels can be used to exchange data wirelessly, making the communication more reliable and immune to potential interference.

3

//Secure connection

Bluetooth technology provides secure communications through encryption and authentication, preventing unauthorized access and ensuring the safety of the vehicle and its occupants. Prior to Bluetooth specification version 5.4, it was not possible to encrypt broadcast data. This is now possible with the new "Encrypted Advertising Data" feature, which is a great addition to PAwR and enables more secure communications.

4

//Low power consumption

Bluetooth LE is essentially a low-power wireless communication protocol. Furthermore, when using PAwR, the central unit periodically sends advertising packets and the observers only listen during these advertising activities while sleeping in between. Replies are only sent when they are required. This is very energy-efficient, especially for battery-powered devices such as electric vehicles.

5

//low cost

Bluetooth LE chips from major suppliers are shipped in very high volumes in a variety of applications, and economies of scale and highly amortized development costs keep selling prices low. Bluetooth LE chips are cheaper than proprietary wireless chips designed for wireless BMS, which have limited economies of scale and lower volumes.

6

//Multiple sources

The benefit of using Bluetooth LE is that multiple suppliers of chips can be used in the supply chain. This allows BMS and electric vehicle manufacturers to have a second source to guarantee mass production needs and continue to respond to price pressure.

BMS is a critical component in the automotive industry, responsible for ensuring that electric vehicles operate efficiently and safely. Wireless BMS is lighter and more flexible than wired devices, and as battery packs continue to change in complexity and size, wireless BMS adoption is increasing. Bluetooth technology, especially Bluetooth LE5.4 with aWR, is an ideal choice for wireless BMS due to its very low power consumption, lower latency, and supply chain advantages brought by the standard's large-scale deployment characteristics. As electric vehicles become more popular, Bluetooth-based wireless BMS will play an important role in ensuring the superior performance and safety of these vehicles.