Centralized Battery Monitoring Systems

Centralized Battery Monitoring Systems

© Fraunhofer IISB
Architecture of centralized battery monitoring systems
© Fraunhofer IISB
Battery monitoring with daisy chaining and active balancing
© Fraunhofer IISB
Battery monitoring with active balancing & redistribution

In centralized battery monitoring architectures, each battery module is equipped with a battery monitoring integrated circuit (IC), typically mounted onto the battery module itself. The monitoring IC acquires the voltage of every single cell and the temperature of each or only some of the cells in the module. It comprises a number of analog-to-digital converters to measure the cell voltages and the temperatures. It is also in charge of the cell voltage balancing. In most cases, a passive balancing method is used, thus allowing a simple balancing circuit by only using a transistor and a resistor. More sophisticated monitoring IC feature an active cell balancing method, where the energy of the most charged cells is redistributed to weaker cells in the module. Further, high-end monitoring IC allows energy redistribution over the entire battery pack. The monitoring IC is controlled by a microcontroller, which preprocesses the data acquired by the monitoring IC and passes it on to the BMS via the internal CAN bus. As the monitoring IC operate at voltage levels up to 450V, the communication and power supply lines have to be galvanically isolated.

The battery monitoring system passes the measurement data on to the higher level battery management system (BMS), commonly via an internal CAN bus (iCAN). The BMS processes the data to determine the current state of the battery, and communicates with the rest of the system via an external CAN bus (eCAN).

In 2011, the worldwide first live-demonstration of active balancing battery monitoring with an integrated circuit from AMS providing energy redistribution in the entire battery pack was performed by Fraunhofer IISB.

Examples of centralized battery monitoring systems developed at Fraunhofer IISB:

Module
Monitoring IC

Module Controller

Module
Additional IC

Balancing
Method

Number of Cells (max)

Atmel ATA6870

Atmel AT90CAN128

Atmel ATA6871

Passive

12 (12)

Atmel ATA6870 Atmel AT90CAN128

Atmel ATA6871

Active

12 (12)

Linear Technology LTC6802 Atmel AT90CAN128

 

Passive

12 (12)

Linear Technology LTC6804 Not needed
(daisy chained)
  Passive
and
Active
12 (12)
AMS AS8505 Atmel AT90CAN128

 

Active

4 (7)

AMS AS8506 Not needed
(daisy chained)
  Active 12 (14)
ON Semiconductor POC Atmel AT90CAN128

 

Passive

4 (12)