Tesla’s massive investments in battery ‘gigafactories’ and Volkswagen’s plan to build six dedicated battery production plants in Europe by 2030 indicate that the battery has become the most strategically important component in the automotive industry.
Car manufacturers’ efforts to reduce the size, weight, and cost impacts of batteries over a vehicle’s complete lifecycle, and to extend the driving range that the battery supports, will have a huge impact on their market share and competitiveness. As increasing numbers of older 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.
The headlines about battery developments tend to highlight research into the new and sometimes exotic materials which might one day be able to store more charge than today’s lithium technology; a completely 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 in fact, new wireless battery management system (wBMS) technology, developed by Analog Devices and pioneered by General Motors in its modular Ultium batteries, promises to give car manufacturers a new competitive edge across the whole of a battery’s life.
This new wire-free technology promises to transform the design, production, servicing, and disposal of EV batteries.
Cost, space, weight, and design problems
In a conventional EV battery, wiring supports communication between each cell in the battery pack and an Electronic Control Unit (ECU) which regulates its operation to ensure that it provides power to the vehicle.
This requirement for communications inside the battery reflects the complex architecture of a large battery pack: it is 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. This is the job of the cell monitoring units in the BMS.
But the data from each cell only become useful when they reach the BMS’s ECU, which controls the way power is supplied to and drawn from the battery, module by module, and maintains the battery’s safety functions. Therefore, an EV’s battery requires a means to transfer data from each module, where voltage, current and temperature are measured, to the ECU’s processor. Traditionally these connections have been made with wires.
But it is not difficult to compile a long list of disadvantages: a copper wiring harness is heavy, and occupies space that, if filled by a battery cell, would give extra energy capacity. Additionally, the connectors can potentially suffer from mechanical failure. 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. Get rid of the wiring harness, and the car manufacturer also gains new flexibility to design the form factor 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 must be assembled, and the connections terminated manually. This is a costly and hazardous process, because high-voltage EV battery modules are supplied charged.
The new modular and scalable wBMS system platform provides OEMs with a fully automated battery pack assembly. After the elimination of the (signal) wiring harness, the only connections which a battery module requires are the power terminals, which can readily be made by robots in an automated process. By eliminating manual labour, OEMs also eliminate the safety risks to assembly line workers.
But the advantages of ADI’s wBMS technology extend beyond the point at which a new car appears for sale.
One is servicing. Secure wireless capability means that the condition of the battery pack can be conveniently analysed by diagnostics equipment 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. Another benefit is 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. And finally, second life. The lifetime of a future EV’s battery will likely exceed that of the vehicle itself. So now 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 creates a new source of value for EV manufacturers, which are responsible for the recycling or disposal of the batteries in scrapped EVs.
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. In combination with data from when the module was originally produced, this allows the optimal usage of second-life modules in their next 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 wireless system
The wBMS technology 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 best-in-class 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.
Unlike consumer-oriented wireless technologies such as Bluetooth or Wi-Fi networking, the wBMS solution puts the emphasis on achieving reliable and secure communication under all operating conditions, thereby complying to the automotive industry’s requirement for reliability, safety, and security.
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 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 ISO 26262 functional safety standard. The system is resilient in noisy environments and provides secure communication between the monitoring units and the manager using sophisticated encryption technology.
Lifetime management
Across the entire battery pack’s lifetime, from initial assembly through disposal to second life, the wBMS solution ensures that the vehicle’s manufacturer and its owner can easily track the condition of the battery, maintain performance and safety, and maximize value.
It is also backed by ADI’s BLIS (Battery Lifecycle Insight Service) technology. This provides edge- and cloud-based 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.
Author details: Norbert Bieler, Director Business Development eMobility, Analog Devices
