Understanding EV battery management system architectures

A battery management system (BMS) ensures safe and efficient energy distribution for electric vehicles (EVs). This article discusses the four primary BMS architectures used in popular EVs, details BMS integration with charging infrastructure, and explores emerging technologies shaping future BMS development.

Understanding BMS architectures

The BMS actively monitors EV batteries to prevent overcharging, over-discharging, overheating, and short-circuiting. It manages the state of charge (SOC), state of health (SOH), and state of temperature (SOT), interfacing with the EV’s main controller to maximize efficiency and performance. This includes optimizing acceleration and regenerative braking and preventing thermal runaway.

Smart battery packs, particularly the more advanced ones, incorporate embedded chargers to expedite rapid charging, with the BMS managing the process for wired and wireless systems.

Figure 1. A schematic of an EV’s BMS depicting the flow from user interface and electrical control to battery state analysis, monitoring, and safety — with integrated communication and thermal management loops for optimized operation. (Image: Cyient)

BMS architectures are categorized into four primary groups:

Centralized BMS: A single controller manages all battery cells and modules, simplifying system design and reducing component count. While this design streamlines management, it may limit scalability for larger battery systems and introduce the potential for a single point of failure.
Distributed BMS: Multiple controllers operate across specific modules or cell groups essential for large batteries requiring individual monitoring. This scalable design enhances system reliability through built-in redundancy.
Modular BMS: Independent units, each capable of autonomous operation, comprise a modular BMS. This scalable configuration facilitates flexibility in battery size and supports the easy addition or removal of modules.
Hybrid BMS: Combining centralized and distributed elements, a hybrid BMS employs a central controller for overall management alongside local controllers at the module level for detailed cell monitoring and control. This structure offers comprehensive system management with granular control capabilities.

The BMS topologies of popular EVs

The Tesla Model S features a centralized BMS topology with a single controller that processes battery cell data. This
paradigm ensures efficient charge and discharge cycles, a maximized driving range, and battery integrity.

Figure 2. An illustration of a Tesla Model S parked in the driveway of a suburban home. The popular EV features a centralized BMS.

Tesla’s Model 3 and Model Y EVs employ advanced BMS designs to optimize battery pack performance. Notably, a limited run of Model Y EVs included a structural battery pack with 4680 cells, indicating a transition toward a more integrated CTB (cell-to-body) approach.

BYD’s Seal also uses CTB technology to enhance BMS performance, vehicle rigidity, and safety. Additionally, some EV manufacturers are exploring cell-to-pack (CTP) designs to increase energy density and simplify manufacturing processes.

In contrast to a centralized BMS, Nissan’s Leaf features a distributed BMS topology with individual controllers managing each battery module. This setup improves overall system efficiency and safety by providing precise management at the module level.

Lastly, BMW’s i3 includes a modular BMS architecture. The battery pack is segmented into distinct modules, each with its own BMS. These individual modules can be serviced independently.

Integration with EV chargers

The seamless integration of a BMS with an EV charger ensures safe and efficient battery charging. Fundamental to this integration is established communication protocols that facilitate data sharing, such as the SOC, SOH, and other key parameters.

A properly integrated charger adjusts its output to battery requirements, dynamically modifying charge rates for optimal efficiency and battery health. The BMS monitors the EV charging process for electrical irregularities, including over-voltage, over-current, or high temperatures. If unsafe conditions are detected, the BMS instructs the charger to reduce or halt charging.

To prevent overcharging as the battery approaches full capacity, the BMS signals the charger to gradually decrease the charging rate, maintaining the battery pack’s integrity and extending its service life.

Future BMS trends and emerging technologies

New technologies and advancements are poised to enhance BMS efficiency and extend battery lifespan, including:

Artificial intelligence (AI): AI refines the precision of battery state estimations and behavior using sophisticated
machine learning (ML) algorithms. Similarly, simulation tools identify precise state estimations, accelerating the
iterative BMS design process.
Wireless BMS: An evolving technology, a wireless BMS simplifies battery management and reduces manufacturing
costs by eliminating physical wiring between battery cells and management systems.
Multi-model co-estimation: This technique provides a detailed understanding of battery conditions, facilitating
precise predictions, efficient charge management, and improved reliability.

Summary

Battery management systems seamlessly integrate with EV chargers to ensure safe and efficient energy distribution. Many popular EVs use one of four primary BMS architectures: centralized, distributed, modular, or hybrid. Evolving technologies, such as AI/ML and wireless BMS, are paving the way for new advancements in battery management.