How Does a Battery Management System Work?

Unlike conventional automobiles with combustion engines that have long supported driving operations, electric vehicles take advantage of powerful lithium batteries that supply the energy and power necessary for standard operations. For a lithium battery to optimally supply automobile systems with the correct range of voltage and current, they utilize what is known as a battery management system (BMS). In this blog, we will discuss battery management systems and their functionalities, allowing you to better understand their importance for EVs.

Battery management systems are a form of embedded system, containing numerous electronic components that are assembled onto a circuit board. These circuit elements may vary in type, ranging from purpose-built electronics to purpose-built software. With the implementation of a battery management system within an electric vehicle, the battery pack and all individual cells can be monitored on various parameters so that performance is optimized and safety risks are averted. For the primary functions of a typical electric vehicle battery management system, such devices promote safety, performance optimization, health monitoring, diagnostics, and communication.

As the standard, most electric vehicles utilize high voltage lithium-ion battery packs. When compared to other various counterparts, lithium-ion battery packs in particular are known for their higher energy density which ranges between 100 and 265 Wh/kg. As a result of such characteristics, lithium-ion battery packs have the potential risk of catching fire during atypical circumstances. To prevent such occurrences, the vehicle’s battery packs will need to always be operating within the constraints of predefined safety limits.

With the battery management system, battery packs are consistently monitored in regard to their temperature, voltage, and current. To uphold ample thermal management, the temperature of the battery is monitored, and safety mechanisms or cooling effects will be actuated as necessary to maintain conditions within safe limits. As thermal runaway is a hazardous condition for such batteries, the BMS is capable of limiting maximum charge and discharge currents. For an example of a real world application, electric vehicles like the Hyundai Kona Electric are designed with automatic power output limitations that activate in the instance that the battery management system detects pack overheating. When this occurs, the car will enter a fail-safe mode to protect the vehicle and its driver.

Alongside safety features, enhancing overall performance is a major aspect of any battery management system. For a lithium-ion battery to function most optimally, its State of Charge (SoC) will have to be kept between minimum and maximum charge limits, that of which may be found in the related battery profile. As overcharging and deep discharging degradation can both decrease the capacity of the battery and its lifespan, the BMS will prevent cell voltages from falling below safe limits during discharging. On the other hand, the BMS also manages the recharging process as well, utilizing regenerative braking for health. Another optimization functionality of a BMS is its cell balancing, that of which is when the system maintains equal voltage levels across all cells to mitigate unequal discharge rates. To best balance rates, the BMS will drain excess energy from more filled cells.

For health monitoring and diagnostics, battery management systems focus on determining the State of Charge and State of Health of the given battery pack. To do this, the system will utilize its readings on temperature, voltage, current, and more. The State of Charge in particular is important, as it allows for the system to monitor the amount of energy that is available so that the distance the vehicle can travel before needing a recharge can be calculated. For the State of Health, on the other hand, the battery management system compares the current conditions of the pack in comparison to the original capacity. If any anomalies or errors are detected, they will be logged so that a remedy may be found upon maintenance and inspection. Additionally, the battery management system will also utilize any mechanisms or actions as required to protect the battery.

The final major role of the BMS is to uphold communication with all other Electronic Control Units present in the vehicle, and this is done to optimize functionality as battery parameters are shared. An example of this is AC charging in which the BMS will work alongside the onboard charger so that ample energy is stored within safe parameters. Meanwhile, for DC charging, the BMS will establish a direct communication link with the EVSE.

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