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Role of battery management systems in battery safety

19 December 2023

Alarming data reveals that two thirds of electric vehicle battery fires occurred when the vehicle was parked. Battery safety is not only crucial during vehicle operation, but also when the vehicle is idle. That is why today we will discuss the critical importance of Battery Management Systems (BMS).

The role of battery management systems (BMS)

A BMS, or Battery Management System, is like the "brain" of a battery, especially in electric vehicles. Its main function is to monitor and control different aspects of the battery to ensure its safe and efficient operation. 

Imagine something like the brain of a battery, which is able to measure, control, etc. Above all, it ensures safety by making decisions. All this makes a difference to the safety of the whole system.

On the one hand, it controls the temperature of the battery to prevent it from getting too hot, which can be dangerous. In addition, it also prevents the battery from being overcharged or over-discharged, which could damage the battery.

In addition, the BMS identifies any problems or faulty cells within the battery and takes action to prevent them from affecting the rest. And thanks to cell balancing, it ensures that all cells in the battery have similar charge levels. 

Ultimately, it is an essential part of making electric vehicles and other battery-powered devices operate efficiently and safely.

Consequently, the battery management system plays a crucial role in making fundamental decisions to safeguard the integrity of the system and handle a large amount of data to perform its functions. However, the premise of "the more data, the better" is not always valid. Adding extra sensors, additional algorithms and complex system logic might seem like a logical choice to improve decision-making, but it can sometimes backfire. 

Lots of data does not equal better decisions

Decision-making involves a detailed process of managing and analysing data. However, this process faces significant challenges:

  • More processing means slower and less accurate decisions.
  • Problems in data traffic can lead to delays and possible errors.
  • More sensors do not guarantee better decisions; the key is a qualitative approach to data acquisition.
  • It is key that the design of the BMS hardware is aligned with the data, so that better decisions can be made.

In short, it is about prioritising strategic data over volume. Too much data is sometimes worse than not enough data, the important thing is quality.

Are all battery fires due to or directly related to the BMS?

While the BMS is crucial to prevent dangerous situations during charging, other factors such as cell defects, mechanical impacts, or external problems can also trigger fires. It is essential to consider various factors and conduct a detailed analysis to determine the exact cause of a battery fire.

Why investigate cell equilibrium as a cause of thermal decontrol?

If some cells receive more charge than others during the charging or discharging process, they may overheat. This thermal runaway can lead to battery degradation, cell failure and even increase the risk of fire.

Understanding and correcting cell balancing is therefore essential to maintain thermal stability and battery safety in applications such as electric vehicles and energy storage systems.

Cell balancing is a fascinating process in which cells are charged to achieve uniform levels. Visualise it as two glasses, one overflowing and one filled to 95% of its capacity. How do we get them both to the same percentage of fullness? With balancing! 

Cell balancing is achieved by passive, active or hybrid methods, controlled by the battery management system (BMS). Active balancing pumps current, passive balancing uses resistors to equalise loads, and hybrid balancing combines both techniques. The right choice of balancing current is crucial to avoid problems such as overcurrent or irregular ageing.

Meticulous design of the balancing mode is essential to avoid problematic situations, especially in non-automotive applications that lack strict regulations. 

The implementation must consider the specific characteristics of each cell, as not all cells behave in the same way. Balancing is done at rest or between load cycles, which means that any event not monitored in time by the BMS could cause thermal problems.

Each circuit design is unique, depending on cell selection and BMS implementation strategy. Neglecting quality or taking shortcuts in testing can have serious consequences.

What factors affect BMS design?

Quantity and Quality

The quantity and quality of sensors used to monitor the cells is a crucial decision, and several factors influence this choice. It is essential to consider aspects such as the adaptability, tolerance, range and sensitivity inherent in each sensor.

Data Upload Frequency

The frequency of data upload to the BMS must be carefully weighed. The rate at which data is updated directly impacts the ability of the system to adapt to changes in battery conditions in real time. Choosing an appropriate upload frequency ensures a fast and efficient response of the BMS to variations in battery status.

Algorithms + Cell Data + System Specification

BMS design relies on advanced algorithms, cell-specific data and system specifications. The selection of efficient algorithms determines how data is processed and utilised, while detailed information on each cell is essential to understand its individual state. Furthermore, harmonious integration with the overall system specifications is crucial to ensure consistent and efficient performance of the BMS.

Balancing Processing Speed with Bandwidth

BMS design involves finding a precise balance between processing speed and available bandwidth (CAN traffic). Agile processing speed is essential for fast and efficient response, while bandwidth determines the speed of data transfer between different system components. Achieving an effective harmonisation of these variables is critical for optimal BMS performance.

Conclusion

Battery safety is a key concern, not only to ensure optimal vehicle performance, but also to address the environmental and safety concerns associated with battery technology. With the growing adoption of electric vehicles, effective implementation of BMS becomes crucial. The goal? Mitigate risks, ensure reliability and extend battery life. Ultimately, it is about contributing to sustainability and safety in the electric mobility landscape.

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