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23/08/2011
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The development of electric, hybrid and plug-in hybrid vehicles is generating huge interest in battery technology. Whilst much of this focus has been on the cells, it is important to understand the role of the Battery Management System (BMS), which is just as critical. In this article Axeon, Europe's leading independent designer and manufacturer of batteries for electric vehicles, outlines the role of the BMS and explains why a flexible system can reduce costs and development time for vehicle manufacturers.
 Both battery and vehicle technology are developing rapidly, so having a control system – the BMS – that is cell-agnostic (i.e. can work with a range of different cell chemistries and form factors) and customisable can deliver clear benefits to the automotive manufacturer. This type of flexible BMS allows the retention of a core system that measures all safety aspects, but one that can be modified to work with different cell chemistries and vehicles. This ensures that OEMs' investment in their BMS is future-proof, vehicle communications and control protocol integration only needing to be performed once in but allowing drop in of new advanced chemistries as and when available.
Cell behaviour varies depending on the chemistry, so the BMS must be able to adapt to different chemistries and is critical in order to accurately measure the state of charge. High power automotive battery applications are still dominated by lithium iron phosphate (because of its high rate capability). It has a very flat voltage profile, which makes state of charge estimation more of a challenge, so only more sophisticated BMS applications can keep track of state of charge. The high energy density electric vehicle market on the other hand is becoming more focused on mixed transition metal oxide chemistries, which have a more sloping voltage profile. This may allow easier state of charge estimation, but may require more complex vehicle control strategy, for example the need to de-rate at low state of charge to avoid detrimental battery performance loss.
Rather than source exclusively from one supplier, Axeon carries out competitive analysis on a range of cells from different suppliers, allowing it to source the optimum cell and form factor for any vehicle application, depending on the type of vehicle and its performance requirements. This sourcing strategy, combined with Axeon's electrochemistry expertise, means that it is able to test cells, develop models and parameterise those for integration in the BMS software. The interface with the vehicle can also be modelled and the same BMS can be modified for use in a range of applications. Therefore if customers subsequently want to move to a new cell chemistry, less development is required, reducing both time and cost.
Axeon's BMS is in use across a wide range of vehicles, proving its capability and versatility; these vehicles range from small city cars such as the Electric Car Corporation's Citroën C1 ev'ie, to large electric vehicles such as the Allied Electric Peugeot eBoxer light commercial vehicle and the Rolls-Royce 102EX Phantom Experimental Electric.
After initial development and deployment of its own BMS in various vehicle applications, Axeon is now working on a new, second-generation BMS, in conjunction with Ricardo, which will be more modular in structure – plug-and-play – and more easily testable on any vehicle model, thus providing a faster route to market.
Axeon has an extensive future battery technology roadmap backed-up by a significant research and development programme. The company's advances into new technologies will lead to smaller, lighter and lower cost Battery Management Systems – and therefore smaller, lighter and lower cost batteries.
For vehicle manufacturers, the advantage in working with Axeon is that the BMS is already proven and in use in a broad range of applications, meaning that there is no requirement to build-up or re-design a bespoke system. OEMs can therefore create a tailored battery system based on Axeon's tried and tested technology.
For more information on Axeon's BMS, visit: http://www.axeon.com/Technology/Battery-Management-System.aspx
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Author
Axeon Ltd
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