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Redefined BMS in electric cars packs more features

Posted: 06 Aug 2014     Print Version  Bookmark and Share

Keywords:Infineon Technologies  BMS  battery management  electric vehicle  MCU 

The particular value of battery management system (BMS) in electric vehicles has been understated. As of the present, the BMS role is mainly seen as charge management and battery cell maintenance. On the contrary, a broader role for the BMS in the vehicle system would help to assure vehicle safety and effective performance over the vehicle's lifetime. Under such a scenario, it is logical to integrate many more control functions.

This redefined BMS will be responsible for battery fault detection and reaction, control and monitoring, system-level thermal management, and security/brand protection. With an appropriate class of MCU used for this higher-level BMS, future functionality such as intelligent energy management also can be implemented.

Like many aspects of automotive electronics, the battery management system in electric vehicles is evolving rapidly.

From its traditional role in charge management and battery cell maintenance, engineers now see the BMS taking on additional functions related to safety requirements, more comprehensive control and monitoring of the charge system, system level thermal management and system security.

BMS

BMS is now taking on additional functions. (Source: Infineon Technologies AG)

Ultimately, this higher functionality may allow OEMs to adapt the BMS for roles now assigned to the vehicle control unit.

The expanded role of the BMS begins with safety. As an electronic system classified in the upper safety categories ASIL C to ASIL D, the BMS is required to achieve a fault detection rate of 97-99 per cent.

Fault reaction times of <10ms to open the main switch relay are needed to avoid high-voltage related incidents. The BMS microcontroller unit (MCU) also must manage such safety functions as leakage current and main switch relay monitoring.

Of course, an independent watchdog element also is incorporated to ensure that switches are set to a safe condition in event of controller failure.

Complex algorithmic schemes for efficient management of the chemical/electrical parameters of high-voltage battery packs will increasingly serve as a differentiator for vehicle OEMs.

As a result, more powerful MCUs with large on-chip memory (up to 4MB of Flash) are needed. Infineon's AURIX 32bit devices are good examples. This class of MCU typically provides additional features that support the new capabilities that are redefining the BMS.

Some of these features represent consolidation of previously separate functionality. A simple 8bit, low-power (uA range) MCU integrated into the larger MCU, and operating in a separate low-power domain, readily handles monitoring of battery charge status using a cyclic wakeup timer.

Active thermal management can be implemented using on-board ADCs and timing functions to monitor parameters and actively control heating and/or cooling actuators (e.g., fan motors, pumps).

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