Wireless Battery Management Systems

Enabling smart battery ecosystems solutions through higher battery performance, greater lifetime and cost value

Stephan Prüfling and Norbert Bieler

Electrification of passenger cars and commercial vehicles is entering a new phase of market penetration. The shift away from technology feasibility demonstration, premium vehicles or small series development towards mass production, technology commercialization and consequently more affordable and technology optimized vehicles is obvious.

Nevertheless, most current generation EVs are still considered as expensive or less attractive when compared to conventional combustion engine cars. Consequently, cost reduction and improved performance is key to ensure a successful and sustainable market growth.

Reduction of size, weight, and cost impact the competitive edge of battery systems over a vehicle’s complete lifecycle. On the other hand, the extension of the driving range will also have a significant impact on their market attractiveness and competitiveness.

Furthermore, as increasing numbers of EVs reach the end of their life, car manufacturers will even be competing for the value to be derived from so called ‘second life’ batteries recovered from scrapped vehicles.

Out of this demand, news about battery innovations tend to highlight the new battery packaging concepts and new materials which might one day be able to store more charge than today’s lithium technology. A different part of the battery – the battery management system (BMS), which monitors the state of charge and health of the battery – tends to go under the radar but needs to follow and support battery innovation.

Here, the new wireless BMS (wBMS) technology, developed by Analog Devices and pioneered by General Motors in its modular Ultium battery platform is now released to mass production. The wBMS gives car manufacturers a new competitive edge across the whole of a battery’s life. Starting from when battery modules are first assembled, to operation in an EV, beyond to disposal, and even -if needed- into the battery’s second life.

Wired Battery connections – the costly, heavy and complex approach 

The intention for the wBMS technology development was based on an analysis of the drawbacks of the communications wiring in today’s conventional EV battery packs. This analysis drew on Analog Devices expertise: it supplies the market’s most accurate BMS ICs and in the wireless communications field. Analog Devices also developed the world’s most robust mesh networking technology for industrial environments.

In a conventional EV battery pack. each cell is measured by a Battery management IC. Data from the Battery Management IC is then communicated back to the pack ECU through wiring. This requirement for communications inside the battery reflects the complex architecture of a large battery pack: it is typically made up of modules, each of which contains multiple cells. Natural production variations mean that each cell has individual characteristics which vary within a specified tolerance range. To maximize battery capacity, lifetime, and performance, the key parameters of battery operation – voltage, charge/discharge current, and temperature – need to be monitored and logged individually for each module.

diagram highlighting the differences between conventional EV battery packs and new wBMS modules.

a typical multi-component wired BMS network (left), and the simpler arrangement made possible by wBMS technology (right)

Fig. 1: a typical multi-component wired BMS network (left), and the simpler arrangement made possible by wBMS technology (right) [Source: Analog Devices, AVL]

This is the reason why an EV’s battery requires a means to transfer data from each module or cell, where voltage and temperature are measured, to the ECU processor (see Figure 1). Traditionally these connections have been made with wires: wired connections have the advantage of being familiar and well understood.

The disadvantage of a wired BMS

But there is also a list of disadvantages related to wires: a copper wiring harness adds additional weight, and occupies space that, if filled by a battery cell, would provide extra energy capacity. Additionally, the wiring needs to be fastened on battery housing structures and connectors can potentially suffer from mechanical failure especially under vibration and shock conditions. In other words, wires increase development effort, manufacturing cost, and weight while also reducing mechanical reliability and usable space. This results in reduced driving range. Remove the wiring harness, and the car manufacturer also gains new flexibility to design the form of the battery pack to fit the design requirements of the vehicle.

The complexity of a battery’s wiring harness also makes the assembly of a battery pack difficult and expensive: wired packs have to be assembled and the connections terminated manually. This is a costly and hazardous process, because high-voltage EV battery modules are supplied charged. To maintain the safety of the assembly process and to protect production line workers, rigorous safety protocols are applied.

Considering all these factors, there are many reasons for OEMs to introduce a robust wireless technology in new EV battery system platforms.

Wireless BMS a new smart approach

The wBMS is a complete solution which is easy for the automotive manufacturer to integrate into a battery pack design. It includes a wCMC (wireless cell monitoring controller) unit for each battery module, and a wireless manager unit to control the communications network which connects multiple battery modules wirelessly to the ECU. Beside the wireless section, each wCMC unit includes a battery management system which performs highly accurate measurements of various battery parameters so that the applications processing unit can analyse the state of charge and state of health of the batteries.

While the wBMS technology has taken full advantage of eliminating the wiring harness design and assembly issue there are further areas inside the battery lifecycle where additional value will be generated:

Battery assembly – the only connections which a battery module requires are the power terminals, which can readily be made in a highly automized process. By eliminating manual labour for assembly and testing, this also avoids safety risks to assembly line workers (see Figure 2). Furthermore, the modules can also be tested and matched before installing inside the battery.

the wBMS eliminates the BMS signal wiring harness to enable automated, robotic production of battery packs

Fig. 2: the wBMS eliminates the BMS signal wiring harness to enable automated, robotic production of battery packs [Source: AVL]

Servicing – secure wireless capability means that the condition of the battery pack can be conveniently analysed by diagnostics equipment in an authorized garage without touching the pack. If a malfunction is detected, a faulty module can easily be removed and replaced. A wireless configuration simplifies installation of a new module in the battery system.

Second life – with the increasing number of vehicles, a market is emerging for ‘second life’ batteries recovered from scrapped EVs and repurposed for applications such as renewable energy storage systems and electric power tools. This additionally creates a new source of value for EV manufacturers, responsible for the recycling or disposal of the batteries in scrapped EVs as wBMS allows a simpler integration of the modules for second life applications.

Disposal – the recyclable metal and potentially hazardous materials inside a battery pack require approved and regulated disposal arrangements. The simple connections and absence of a communications wiring harness make removal of battery modules easier and quicker than that of a wired battery.

Data management – the wBMS technology makes it easy to read out critical battery data from each intelligent module: this means that the condition of the batteries can be determined individually. This data can, for instance, provide information about the state-of-charge (SOC) and state-of health (SOH) of a module. In combination with data from when the module was originally produced, this allows the optimal usage in their second life application, and the provision of a detailed set of specifications for each module on sale. The ready availability of these data increases the resale value of the modules.

Complete solutions for wireless battery management systems by Analog Devices

The wireless network protocol implemented in the wBMS system meets the automotive industry’s requirement for reliability, safety, and security under all operating conditions based on network-wide time synchronization technology. The use of the wBMS in a mass production EV from General Motors is proof of its reliability in the harshest environments: the wBMS-based battery has been driven hundreds of thousands of kilometres in more than 100 test vehicles, on- and off-road, and in environments ranging from desert to the frozen north and under the toughest conditions.

The wBMS, also supports automotive manufacturers’ programs for compliance with the ISO26262 functional safety standard. The radio technology and the networking protocol have been developed in such a way that the system is resilient in noisy environments and provides secure communication between the monitoring units and the manager, using sophisticated encryption technology. The security measures avoid spoofing of data transmitted on the wireless network by an unintended recipient such as a criminal or hacker. Furthermore, the transmitted data is received without any modification of the contents, and the intended recipient knows exactly which source has sent a message.

Lifetime management of the value of the battery

Across the entire battery pack’s lifetime, from initial assembly through disposal to second life, the wBMS capability embedded in the battery pack ensures that the vehicle’s manufacturer and its owner can easily track the condition of the battery, maintain performance and safety, and maximize value.

The wBMS technology is also backed by BLIS (Battery Lifecycle Insight Service) technology. This provides edge- and cloud-based data software to support traceability, production optimization, monitoring in storage and transit, early failure detection, and lifetime extension. Together, the wBMS and BLIS technologies enable automotive manufacturers to gain higher returns on their investments in battery pack development and production, improve the economics of their electric vehicle business strategies, and help accelerate the market’s shift towards a low-carbon, sustainable future for personal mobility.

The key to design and enable such battery solutions with wBMS are system understanding, methods and tools that support the design and technologies as described here. Together with Analog Devices, AVL is working to provide smarter BMS solutions to their customers all over the world by combining the strength of both companies.

Stephan Prüfling (Product Manager Battery Management Systems, AVL)

Norbert Bieler (Director Business Development eMobility, Analog Devices,)

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