Battery Management Systems play a critical role in current and next generation battery packs

The electrified systems powering vehicles, machines and the green buildings and industries of the future will require energy storage systems that can deliver power reliably whilst remote from an electrical grid connection or when connected to intermittent energy harvesting sources such as solar and wind power. A practical energy storage solution for most applications will be a rechargeable battery, typically a Lithium based system. To maximise the efficiency, lifetime and to ensure the safety of the battery, a good battery management system (BMS) is crucial.

Matthew Johnson, Divisional Marketing Manager at Anglia takes a look at a highly integrated BMS solution from Analog Devices and gives an insight into a new product development which is already gaining acceptance with major automotive manufacturers and will debut on upcoming EV platforms.

Typically the BMS oversees many critical functions of the rechargeable battery pack including but not limited to protecting the battery from operation outside its safe parameters, controlling environmental variables such as temperature, monitoring charge and discharge states, calculating capacity, authenticating the battery is the correct fitment and reporting all of this data to a host system.

It is clear to see why the BMS is a critical part of any rechargeable battery powered system and careful consideration must be given to its design and the selection of components. Fortunately, Analog Devices have vast experience in the field of battery powered systems and have a wide range of innovative products available for designers to choose from to optimise their battery pack solution.

Analog Devices’ portfolio offers a family of parts for achieving a well maintained BMS; LTC681x cell monitors, LTC2949 fuel gauge and the LTC6820 to provide isolated communications to these devices over the ruggedized communications standard of isoSPI.

Analog Devices’ stackable LTC681x family of multicell battery monitors can measure individual voltages of 6, 12, 15, or 18 series-connected battery cells with a total measurement error of just 1.2 to 2.2mV. The LTC681x devices cell measurement range of 0V to 5V makes the family suitable for use with the majority of battery chemistries available on the market. Cell measurement of all connected cells achieved in less than 290µs, lower data acquisition rates can also be selected for high noise reduction. The LTC681x can be powered directly from the battery pack or from an isolated supply. The battery monitor provides passive balancing and PWM duty cycle control each cell in the pack and includes the ability to perform measurements on redundant cells.

Fig 1. Typical BMS front end solution

Figure 1 demonstrates the LTC2949 in a low-side current sensing configuration, where the isoSPI communication lines are parallel with the bottom LTC6811-1 battery monitor. To enhance reliability, a dual communication scheme can be implemented by connecting a second isoSPI transceiver to the top of the battery stack therefore creating a ring topology that can communicate in both directions. Isolated communication with the SPI master controller is achieved using the LTC6820 isoSPI-to-SPI signal converter.

The LTC2949 device accurately interprets the charge and energy flowing in and out of a battery pack by simultaneously monitoring the voltage drop over up to two sense resistors and the battery pack voltage. The device can be configured to sense current on the high or low side of the system and can achieve an impressive 0.3% current and voltage measurement accuracy.

Utilising low offset Sigma Delta true average ADCs ensures the device takes accurate measurement of voltage and current with minimal power loss. The continuous integration of current and power also ensures lossless tracking of charge and energy delivered or received by the battery pack. Energy and charge accuracy of 1% can be realised with the LTC2949 device.

Modular battery packs require a wiring harness. This wiring harness must be tolerant of electromagnetic interference and needs to be isolated. Historically, the best solution for this has been to utilise the CAN communication standard along with some form of isolation. Analog Devices’ isoSPI interface is a proprietary physical layer adaptation of the standard chip-level SPI that unleashes the full potential of cost-effective distributed-pack architectures. Designed for use in high voltage and high noise systems, isoSPI provides safe and reliable data transfer of up to 1 Mbps over up to 100 meters of single twisted pair cable, using a simple pulse transformer. isoSPI offers a cost-conscious alternative to other on-board isolation solutions.

Functional Safety Management

Analog Devices’ have developed this ISO 26262 compliant platform further with the addition of the recently released ADBMS6815 multicell battery monitor which features diagnostic coverage to enable ASIL D rated systems.

The future of Battery Management

Notwithstanding the existing array of industry leading BMS solutions, Analog Devices continue to innovate with their next generation of products which includes the recent announcement of the industry’s first wireless battery management system (wBMS), Fig.2.

Analog Devices have carefully developed wBMS to meet the demanding requirements of the global automotive industries next generation EV platforms, it simplifies battery pack construction whilst allowing design flexibility and reuse across different vehicles, increased battery pack energy density and optimised range, mechanical reliability and all important lower overall system cost.

Analog Devices new wBMS enables automotive manufacturers the increased flexibility to scale their electric vehicle fleets into volume production across a wide range of battery platforms and vehicle classes.

Fig. 2 - wBMS example implementation

The implementation of the Analog Devices wBMS allows for elimination of the need for a traditional wired harness, this can save up to 90% of the wiring typically required and up to 15% of the volume in the battery pack, saving valuable space and reducing weight as well as improving design flexibility and manufacturability, without compromising vehicle range and accuracy over the life of the battery.

The Analog Devices wBMS includes all integrated circuits, hardware and software for power, battery management, RF communication, and system functions in a single system-level product that supports ASIL-D safety and module-level security building upon Analog Devices proven industry leading BMS battery cell measurement technology. By delivering high accuracy across the entire lifetime of the vehicle battery, the wBMS enables maximum energy use per cell required to achieve the best vehicle range and supports new generation safe and sustainable zero-cobalt battery chemistries, such as lithium iron phosphate (LFP).

Additional system features enable batteries to measure and report their own performance, increasing early failure detection, and enabling optimized battery pack assembly. The data can be monitored remotely throughout the battery lifecycle – from assembly to warehouse and transport through to installation, maintenance and into a second-life phase.

This is the industry’s first wireless battery management system available for production electric vehicles and will debut on upcoming production EV platforms from a globally recognised automotive manufacturer. By bringing this breakthrough system innovation to market, Analog devices are helping to accelerate the entire industry towards a more sustainable future.

Design Support

Anglia offers comprehensive design support via its team of fully trained FAE’s and offers evaluation hardware for the full Analog Devices portfolio including the innovative BMS product range.

There is an extensive suite of demonstration boards available including three differing boards for the LTC2949 integrated current, voltage, and charge monitor, five demo boards for the LTC6820 isoSPI isolated communications interface and LTC681x multicell battery monitor. These demo boards cover all aspects of the battery management system and can be used together in different configurations allowing designers to cater for a multitude of system architectures.

Anglia offer support for customer designs with free evaluation kits, demonstration boards and samples of Analog Devices products via the EZYsample service which is available to all registered Anglia Live account customers.

Anglia’s engineering team have extensive experience of working with battery management systems and can offer component advice and system level support to designers. This expertise is available to assist customers with all aspects of their product design, providing hands on support and access to additional comprehensive Analog Devices resources including technical application notes and reference designs.

Visit www.anglia-live.com to see the full range of other Analog Devices products available from Anglia