The battery management system (BMS) in electric vehicles is typically narrowly defined. The BMS role today is principally seen as charge management and battery cell maintenance.
In contrast, 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.
Battery management system evolution
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, as illustrated in Figure 1.
BMS is now taking on additional functions.
(Source: Infineon Technologies AG)
Click here for larger image
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 to 99%.
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 4 MB of Flash) are needed. Infineon's AURIX 32-bit 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 8-bit, low-power (µA 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).
Security schemes based on cryptography algorithms present exciting opportunities for new capabilities in the BMS. These take advantage of MCUs with an integrated hardware security module (HSM).
For example, the battery can be protected from third-party tampering such as aftermarket replacement of battery cells. Relevant parameters, essentially a digital "fingerprint" of each battery cell, can be stored in a secure, memory-protected area. Cryptography algorithms can utilize the HSM for additional capabilities, such as comparing the amount of charge recorded by the BMS and the amount charged to a customer to ensure accurate billing.
Assured authentication also may be a part of future vehicle-to-grid communications, for example, in demand response charging schemes.
Another emerging application is a vehicle energy management concept that takes advantage of intelligence in the powertrain, in-car navigation unit, and communications to traffic information sources (sensors and even other cars).
Real-time traffic and road condition information, combined with knowledge of trip destination, will make it possible to compare energy needed for specific route choices available and recommend the most efficient route.
With increased capability of the BMS, OEMs can reevaluate the electronic topology of hybrid and all-electric vehicles. Many current designs utilize both an inverter control unit and a separate vehicle control unit to manage higher-order driving strategies.
An architecture that distributes VCU tasks into the inverter controller and BMS can reduce the overall cost for vehicle electronics. The prerequisite for this is the capability of the BMS to support broader functionality in terms of available memory and real-time performance. These functional requirements are met by today's most advanced automotive MCUs, creating new opportunities for innovation in vehicle design.
— Klaus Scheibert is Principal of Powertrain Electronics within the Automotive division at Infineon Technologies AG, Neubiberg, Germany.