Next Generation Battery Management Systems for Automotive Lithium Batteries | George Paterson, Customer Solutions & Programme Director, Dukosi Limited

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Based in Edinburgh, UK, Dukosi is bringing new disruptive technology to market. Its novel battery management system (BMS) provides many benefits that are recognized across the whole battery supply chain, from cell manufacture to eventual recycling. This article focuses on the challenges that electric and hybrid vehicle manufacturers are facing in relation to design, implementation and functionality of current BMS and offers some possible solutions.

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George Paterson, Customer Solutions & Programme Director, Dukosi Limited

To support the growth in plug-in vehicles, lithium batteries have become increasingly larger in charge capacity and voltage. The demand for electric and hybrid vehicles means that battery use is set to rise exponentially over the coming years. The BMS is the control system that manages lithium cells and is a combination of electronics hardware and software. Among its many features, the BMS monitors the voltage and temperature of individual cells, which are critical to the safe operation of the battery system.

The problem with existing BMS

Current BMS solutions lack flexibility, are expensive and complex to design and implement, and can suffer from reliability issues, primarily due to the amount of wiring and connectors used. Furthermore, they do not typically provide the granularity of data needed to optimise system performance and cost, or to support second life applications, which are becoming increasingly important as vehicle manufacturers are responsible for recycling of the battery.

Architecturally, current BMS mostly follow a very similar distributed design. One electronics module takes on the role of a master controller, making all the key decisions from the information that it receives from the cell module units. These cell module units are connected to the many cells in a battery pack by wires that monitor voltage and temperature.

In a B- or C-class sized electric vehicle, 150-180 metres of wire could be required with up to 1,400 physical connections. These wiring harnesses are often the cause of many reliability and safety issues during assembly and use of the battery system, and makes servicing and recycling difficult and expensive. The wiring harnesses can weigh up to 10kg and are expensive due to the number of connectors and the manual assembly methods required to manufacture them.

Another feature of the BMS is to measure state of charge (SoC) and state of health (SoH) of a battery. This is done by measuring several parameters of the cells and the complete system. The accuracy of measurements varies between systems, and hence the SoC and SoH calculation can vary. This influences the accuracy of the “fuel gauge” in the vehicle, which can limit driving range and the efficiency of rapid charging.

A new approach to BMS

There are now new, disruptive BMS architectures available. These systems attach a microchip inside each cell, to create a truly distributed system. The microchip, or Application Specific Integrated Circuit (ASIC), accurately measures the temperature, voltage and current at the cell itself. The ASIC is not just a monitor or measuring device, it also has an inbuilt processor to calculate the SoC and SoH for every individual cell using a cell model that is programmed in during manufacture. This makes for more accurate SoC and SoH calculations which can be used to improve electric vehicle range and optimise rapid charging, while still maintaining the cells within their safe operating range.

Wireless communication

An important feature of this new approach to BMS is that it communicates wirelessly with the master controller, replacing several hundred metres of wiring and many connections with a simple antenna and just two connections. This greatly reduces the complexity of the battery, improves reliability, removes weight, reduces design and assembly time of the battery, and provides much more flexibility to optimise space and weight distribution.

The ASIC also contains memory, meaning that information about the cell, the manufacturer, date of manufacture, test data, chemistry, and capacity can be stored, along with ongoing SoH tracking and recording of any ‘unusual events’ during the cell’s life. This data can also be used to determine the quality of cells once the battery has reached its end of life in a vehicle application. Traditional methods of testing to determine the quality are costly and labour intensive, and residual values are hard to determine. Vehicle manufacturers are liable for batteries at end of life, so any unknown residuals are a liability.

Provenance is key

In today’s automotive market there is a significant problem with a growing number of fake brake and suspension components in vehicles. This will no doubt become the same with electric vehicles and battery packs, and so the provenance of a cell is increasingly important.

It is beneficial for a vehicle manufacturer to be able to quickly and efficiently determine if non-OEM parts have been substituted or prove the authenticity of a battery and cells before repairing a battery under warranty. Because the ASIC is permanently attached to the cell it is not possible to operate a battery without each cell having a genuine microchip. This protects the vehicle manufacturer’s reputation and importantly the safety of drivers, service engineers and battery recyclers.

Much is reported about the development and improvements in cell chemistry to improve range, safety and cost of electric vehicle batteries. However, there is more focus now on the electronics, hardware and software that can offer improvements to electric vehicles. Modern advancements in battery management systems are primed to deliver cost, reliably and operational benefits to electric vehicles.

George Paterson,
Customer Solutions & Programme Director,
Dukosi Limited

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