In our modern landscape filled with electric vehicles, portable electronics, and IoT technology, the efficiency and reliability of battery systems are of paramount importance. Behind the scenes, Battery Management Systems (BMS) play a crucial role in ensuring the optimal performance, safety, and longevity of battery packs. This blog post will explore the intricacies of Battery Management Systems, shedding light on balancing methods, pack measurement techniques, and different architectures used.
A Battery Management System is a sophisticated electronic control unit designed to monitor and manage the health, performance, and safety of a battery pack. It acts as the brain of the system, collecting data from individual cells, managing charging and discharging processes, and safeguarding against overcharging, over discharging, and overheating. To that end, several sensors throughout the pack measure key variables, such as the temperature, voltage, and current.
BMS Components
Temperature sensing in a battery pack is crucial for safety and performance of the battery pack. In an over-temperature condition, the pack must be able to be shut down to prevent thermal runaway. Most packs use direct thermal measurements, such as thermistors or thermocouples. For large scale, high production volume battery packs (such as in EVs), temperature sensors are of high cost. For this reason, many automakers have strived to improve their software models that predict overall temperatures of the pack from only a limited number of temperature sensors as well as voltage and current readings.
Current sensing is important to measuring pack output and determining the performance of the pack over time. It is also critical to be measured to prevent over-current condition, and control current output for thermal throttling if desired. Current sensing is generally done in one of two ways - a loop style hall effect sensor, which measures magnetic fields generated from large currents in the overall battery output wire; or with shunt resistors, which measure voltage over a high-resistance element connected to the output of the overall battery pack.
Several variables, such as the SoC (State of Charge) and SoH (State of Health) are estimated from measured variables. The SoC can be inferred from overall voltage readings on a pack and is a percentage representing the amount of energy stored within the cells compared to their theoretical maximum capacity. For clarity, most packs are never discharged to their minimum, or charged to their maximum. The 0% and 100% you tend to see on your battery powered devices are in fact truncating the maximum and minimum range of the battery in order to save battery health over time and keep the battery in a safe condition. The SoH is calculated when the battery is under changing current. In this condition, the pack can use current and voltage readings to infer an ESR (Equivalent Series Resistance) for each cell in the battery pack. As batteries age, and with increased use, the ESR increases. Increased ESR leads to power losses, loss of capacity, and increased battery heating [4].
Balancing Strategies
Battery cells within a pack are prone to variations in performance due to manufacturing tolerances, aging, and environmental conditions. Over repeated cycles, the differences in performances would lead to a drift in cell SoC between cells within the pack. Balancing ensures that each cell maintains a similar state of charge, preventing overcharging or over discharging of any individual cell. This is crucial for maximizing the overall lifespan and performance of the battery pack.
Passive balancing involves the use of resistors or other dissipative elements to equalize the voltage across cells. While cost-effective, passive balancing is less efficient, slower, and generates significant heat during the balancing process in the passive components used for balancing.
Active balancing utilizes additional circuitry, such as transformers or inductors, to redistribute energy among cells actively. This method is more efficient than passive balancing, resulting in faster and more precise balancing.
BMS Architectures
In a distributed BMS architecture, each battery module or cell incorporates its own monitoring and control system. These local systems communicate with each other to share information and make collective decisions. Distributed architectures offer redundancy and fault tolerance, as a failure in one module does not necessarily affect the entire system.
A centralized BMS, on the other hand, consolidates all monitoring and control functions into a single unit. This centralized approach provides a holistic view of the entire battery pack, enabling more effective management and optimization. However, it comes with challenges related to scalability, complexity, and potential single points of failure.
Distributed BMS
Pros:
Redundancy and fault tolerance.
Scalability for large battery packs.
Localized decision-making for faster responses.
Cons:
Increased complexity in communication between modules.
Higher component count.
Challenges in achieving synchronization between modules.
Centralized BMS
Pros:
Holistic view of the entire battery pack.
Simplified communication architecture.
Potential for optimized control strategies.
Cons:
Single point of failure.
Challenges in scalability for large battery packs.
Increased complexity in wiring and communication.
Battery Management System ICs
Application-specific integrated circuits (ASICs) for battery management systems have become increasingly popular and available with the rise of electric vehicles. Companies such as STMicroelectronics, Analog Devices, Texas Instruments, Infineon and Nexperia (as well as no doubt many others) are all making ASICs specifically designed to measure temperatures, current, and voltages throughout battery packs, all while saving costs and reducing complexity.
The Future of Battery Management Systems
As battery technology continues to advance, the role of Battery Management Systems will become even more critical. The industry is witnessing ongoing research and development efforts to improve balancing methods, enhance measurement accuracy, and optimize BMS architectures. Interesting new technologies, such as Analog Devices’ wBMS (Wireless BMS) system are finding new and exciting ways to improve on existing battery management technologies [3]. As EVs, wireless devices, and grid scale battery storage become more common, the field of battery management systems is sure to evolve and change greatly over the coming years.
In the dynamic world of energy storage, electric vehicles, and portable electronics, Battery Management Systems serve as the silent guardians, ensuring the efficient and safe operation of battery packs. As technology evolves, finding the right combination of balancing methods, measurement techniques, and BMS architectures becomes crucial for unlocking the full potential of batteries and driving the sustainable energy future. The future of BMS technology lies in innovation and continuous improvement, paving the way for more reliable, efficient, and sustainable energy storage solutions.
Sources
[1] “Battery and Energy Technologies.” Battery Management and Monitoring Systems BMS, www.mpoweruk.com/bms.htm.
[2] Keerthi, Sravan Kumar. “Battery Management System in Electric Vehicles.” Cyient, www.cyient.com/blog/battery-management-system-in-electric-vehicles.
[3] Bieler, Hartanto-Doeser “WBMS Technology: The New Competitive Edge for EV Manufacturers.” wBMS Technology: The New Competitive Edge for EV Manufacturers | Analog Devices, www.analog.com/en/thought-leadership/wbms-tech-competitive-edge.html.
[4] Pikkarainen, Jussi. “What Is ESR and Why Does It Matter? Part 2.” Skeleton Technologies, Skeleton Technologies GmbH, 3 Aug. 2023, www.skeletontech.com/skeleton-blog/why-does-esr-matter.
In our modern landscape filled with electric vehicles, portable electronics, and IoT technology, the efficiency and reliability of battery systems are of paramount importance. Behind the scenes, Battery Management Systems (BMS) play a crucial role in ensuring the optimal performance, safety, and longevity of battery packs. This blog post will explore the intricacies of Battery Management Systems, shedding light on balancing methods, pack measurement techniques, and different architectures used.
A Battery Management System is a sophisticated electronic control unit designed to monitor and manage the health, performance, and safety of a battery pack. It acts as the brain of the system, collecting data from individual cells, managing charging and discharging processes, and safeguarding against overcharging, over discharging, and overheating. To that end, several sensors throughout the pack measure key variables, such as the temperature, voltage, and current.
BMS Components
Temperature sensing in a battery pack is crucial for safety and performance of the battery pack. In an over-temperature condition, the pack must be able to be shut down to prevent thermal runaway. Most packs use direct thermal measurements, such as thermistors or thermocouples. For large scale, high production volume battery packs (such as in EVs), temperature sensors are of high cost. For this reason, many automakers have strived to improve their software models that predict overall temperatures of the pack from only a limited number of temperature sensors as well as voltage and current readings.
Current sensing is important to measuring pack output and determining the performance of the pack over time. It is also critical to be measured to prevent over-current condition, and control current output for thermal throttling if desired. Current sensing is generally done in one of two ways - a loop style hall effect sensor, which measures magnetic fields generated from large currents in the overall battery output wire; or with shunt resistors, which measure voltage over a high-resistance element connected to the output of the overall battery pack.
Several variables, such as the SoC (State of Charge) and SoH (State of Health) are estimated from measured variables. The SoC can be inferred from overall voltage readings on a pack and is a percentage representing the amount of energy stored within the cells compared to their theoretical maximum capacity. For clarity, most packs are never discharged to their minimum, or charged to their maximum. The 0% and 100% you tend to see on your battery powered devices are in fact truncating the maximum and minimum range of the battery in order to save battery health over time and keep the battery in a safe condition. The SoH is calculated when the battery is under changing current. In this condition, the pack can use current and voltage readings to infer an ESR (Equivalent Series Resistance) for each cell in the battery pack. As batteries age, and with increased use, the ESR increases. Increased ESR leads to power losses, loss of capacity, and increased battery heating [4].
Balancing Strategies
Battery cells within a pack are prone to variations in performance due to manufacturing tolerances, aging, and environmental conditions. Over repeated cycles, the differences in performances would lead to a drift in cell SoC between cells within the pack. Balancing ensures that each cell maintains a similar state of charge, preventing overcharging or over discharging of any individual cell. This is crucial for maximizing the overall lifespan and performance of the battery pack.
Passive balancing involves the use of resistors or other dissipative elements to equalize the voltage across cells. While cost-effective, passive balancing is less efficient, slower, and generates significant heat during the balancing process in the passive components used for balancing.
Active balancing utilizes additional circuitry, such as transformers or inductors, to redistribute energy among cells actively. This method is more efficient than passive balancing, resulting in faster and more precise balancing.
BMS Architectures
In a distributed BMS architecture, each battery module or cell incorporates its own monitoring and control system. These local systems communicate with each other to share information and make collective decisions. Distributed architectures offer redundancy and fault tolerance, as a failure in one module does not necessarily affect the entire system.
A centralized BMS, on the other hand, consolidates all monitoring and control functions into a single unit. This centralized approach provides a holistic view of the entire battery pack, enabling more effective management and optimization. However, it comes with challenges related to scalability, complexity, and potential single points of failure.
Distributed BMS
Pros:
Redundancy and fault tolerance.
Scalability for large battery packs.
Localized decision-making for faster responses.
Cons:
Increased complexity in communication between modules.
Higher component count.
Challenges in achieving synchronization between modules.
Centralized BMS
Pros:
Holistic view of the entire battery pack.
Simplified communication architecture.
Potential for optimized control strategies.
Cons:
Single point of failure.
Challenges in scalability for large battery packs.
Increased complexity in wiring and communication.
Battery Management System ICs
Application-specific integrated circuits (ASICs) for battery management systems have become increasingly popular and available with the rise of electric vehicles. Companies such as STMicroelectronics, Analog Devices, Texas Instruments, Infineon and Nexperia (as well as no doubt many others) are all making ASICs specifically designed to measure temperatures, current, and voltages throughout battery packs, all while saving costs and reducing complexity.
The Future of Battery Management Systems
As battery technology continues to advance, the role of Battery Management Systems will become even more critical. The industry is witnessing ongoing research and development efforts to improve balancing methods, enhance measurement accuracy, and optimize BMS architectures. Interesting new technologies, such as Analog Devices’ wBMS (Wireless BMS) system are finding new and exciting ways to improve on existing battery management technologies [3]. As EVs, wireless devices, and grid scale battery storage become more common, the field of battery management systems is sure to evolve and change greatly over the coming years.
In the dynamic world of energy storage, electric vehicles, and portable electronics, Battery Management Systems serve as the silent guardians, ensuring the efficient and safe operation of battery packs. As technology evolves, finding the right combination of balancing methods, measurement techniques, and BMS architectures becomes crucial for unlocking the full potential of batteries and driving the sustainable energy future. The future of BMS technology lies in innovation and continuous improvement, paving the way for more reliable, efficient, and sustainable energy storage solutions.
Sources
[1] “Battery and Energy Technologies.” Battery Management and Monitoring Systems BMS, www.mpoweruk.com/bms.htm.
[2] Keerthi, Sravan Kumar. “Battery Management System in Electric Vehicles.” Cyient, www.cyient.com/blog/battery-management-system-in-electric-vehicles.
[3] Bieler, Hartanto-Doeser “WBMS Technology: The New Competitive Edge for EV Manufacturers.” wBMS Technology: The New Competitive Edge for EV Manufacturers | Analog Devices, www.analog.com/en/thought-leadership/wbms-tech-competitive-edge.html.
[4] Pikkarainen, Jussi. “What Is ESR and Why Does It Matter? Part 2.” Skeleton Technologies, Skeleton Technologies GmbH, 3 Aug. 2023, www.skeletontech.com/skeleton-blog/why-does-esr-matter.