What Are the Benefits of Wireless Battery Management Systems?

This article is published by EE Power as part of an exclusive digital content partnership with Bodo’s Power Systems.

The electrification of passenger cars and commercial vehicles is entering a new phase of market penetration. The shift from feasibility demonstration to mass production of premium vehicles is obvious. The commercialization of technology leads to more optimized and affordable vehicles.

Nevertheless, most electric vehicles (EVs) are still considered expensive or less attractive compared to conventional combustion engine cars. Consequently, cost reduction and improved performance are key to ensuring successful and sustainable market growth. Size, weight, and cost reductions 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 significantly impact 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 derived from second-life batteries recovered from scrapped vehicles.

News about battery innovations tends to highlight the battery packaging concepts and materials that might one day 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 (SOC) and state of health (SOH) of the battery—tends to go under the radar but needs to follow and support battery innovation.

The wireless BMS (wBMS) technology, developed by Analog Devices and pioneered by General Motors in its modular Ultium battery platform, gives car manufacturers a new competitive edge across the whole of a battery’s life—starting from when battery modules are first assembled through disposal and even the battery’s second life.

 

Figure 1. A typical multi-component wired BMS network (left) and the simpler arrangement made possible by wBMS technology (right). Image used courtesy of Bodo’s Power Systems [PDF]

 

Wired Battery Connections

The intention of the wBMS technology development was based on analyzing the drawbacks of the communications wiring in conventional EV battery packs. In a conventional EV battery pack, each cell is measured by a battery management IC. Data from the battery management IC are 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 each cell has individual characteristics that 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—must be monitored and logged individually for each module.

This is why an EV 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

However, there is 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 reducing mechanical reliability and usable space. This results in reduced driving range. By removing the wiring harness, the car manufacturer gains new flexibility to meet a vehicle’s design requirements for the form factor of its battery pack.

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

So there are strong reasons for OEMs to introduce robust wireless technology in new EV battery system platforms.

 

Wireless Battery Management Systems

The wBMS is easy for the automotive manufacturer to integrate into a battery pack design. It includes a wireless cell monitoring controller (wCMC) unit for each battery module and a wireless manager unit to control the communications network, which connects multiple battery modules wirelessly to the ECU. Besides the wireless section, each wCMC unit includes a BMS that performs highly accurate measurements of various battery parameters so the applications processing unit can analyze the SOC and SOH of the batteries.

While the wBMS technology has taken advantage of eliminating the wiring harness design and assembly issue, there are other areas within the battery lifecycle where additional value will be generated.

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

 

Figure 2. The wBMS eliminates the BMS signal wiring harness to enable automated, robotic production of battery packs. Image used courtesy of Bodo’s Power Systems [PDF]

 

• Servicing — secure wireless capability means the condition of the battery pack can be conveniently analyzed by diagnostics equipment in an authorized garage without touching the pack. A faulty module can easily be removed and replaced if a malfunction is detected. A wireless configuration simplifies the installation of a new module in the battery system.
• Second life — to 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 also creates a new source of value for EV manufacturers, which are responsible for recycling or disposing of the batteries in scrapped EVs since 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 removing battery modules easier and quicker than a wired battery.
• Data management — the wBMS technology makes it easy to read out critical battery data from each intelligent module: this means the condition of the batteries can be determined individually. These data can, for instance, provide information about the SOC and SOH of a module. Combined with data from when the module was originally produced, this allows optimal usage in its 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.

 

Automotive Industry Requirements

The wireless network protocol 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 run over hundreds of thousands of kilometers in more than 100 test vehicles, on-road and off-road, and in environments ranging from a desert to the frozen north and under the toughest conditions.

The wBMS also supports automotive manufacturers’ programs in compliance with the ISO 26262 functional safety standard. The radio technology and the networking protocol have been developed to make the system resilient in noisy environments and provide 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 are received without modifying the contents, and the intended recipient knows exactly which source has sent a message.

 

Lifetime Battery Management

Across the entire battery pack’s lifetime, from initial assembly through the disposal to second life, the wireless capability embedded in the battery pack ensures the vehicle’s manufacturer and owner can easily track the battery's condition, maintain performance and safety, and maximize value. The entire system, including the interactions between the battery modules’ cell monitoring units and the ECU, is handled by ADI’s technology, with configuration settings defined by the manufacturer.

The wBMS technology is backed by ADI’s battery lifecycle insight service (BLIS) technology. This provides edge-based 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 investments in battery pack development and production, improve the economics of EV business strategies, and help accelerate the market’s shift toward a low-carbon, sustainable future for personal mobility.

The key to designing and enabling such battery solutions with wBMS is system understanding and methods and tools supporting the design and technologies. AVL offers a full range of simulation, testing, engineering capabilities, and experience to drive these innovations and bring them into the market successfully. AVL is working on battery ecosystem solutions by developing data analytics methodologies, predictive functionalities supported by virtual development, and vehicle and battery data to increase battery lifetime and performance.

ADI and AVL are working to provide smarter BMS solutions to customers worldwide by combining the strengths of both companies.

 

This article originally appeared in Bodo’s Power Systems [PDF] magazine and is co-authored by Stephan Prüfling of AVL and Norbert Bieler of Analog Devices.