The Evolving Role of Battery Management Systems
In January 2024, Elon Musk’s Neuralink announced that a microchip had been successfully implanted in a human brain. This microchip is equipped with hundreds of sensing wires attached to the brain, reading electrodes, and translating electrical activities using AI techniques. In the future, this technology could enable disabled individuals to control robotic devices and use their paralyzed limbs again.
In the battery world, a Battery Management System (BMS) incorporates a microprocessor that significantly enhances capabilities and flexibility. Embedded within a battery pack, the BMS connects via sensing wires to the positive and negative terminals of battery cells to read their voltage. It also monitors the current and temperatures of the battery. Algorithms process all these sensed values to estimate the battery’s state at any given time. Additionally, it disconnects the battery power under certain conditions.
Key Factors Shaping Next-Gen BMS
BMS-embedded batteries are found in a wide range of applications, including Electric Vehicle (EV), mWh/kWh Energy Storage Systems (ESS), portable power banks, Uninterruptable Power Supplies (UPS), and consumer robotics, to name just a few. The requirements for each depend on the environment in which they operate. For instance, EV battery systems must withstand the impacts of harsh kinetic dynamics, while ESS may require zero-downtime performance. Cost considerations largely influence consumer batteries.
The steering of the BMS is based on three key factors: safety, performance, and costs. The BMS is an electronic and electrical system with a predefined lifespan and specific failure rate. The longer the required lifespan and the lower the acceptable failure rate, the higher the costs. Additionally, the broader the operational boundary, the more requirements must be met, leading to an increase in costs. Despite the interplay of these factors, the BMS's technical functions remain unchanged.
BMS Architecture
Let’s look into the blueprint of a BMS architecture and break down its main components and their roles. The figure below shows a battery schematic, including a BMS, battery cells, and peripherals.
Cells and Cell Monitoring Sections: Each cell (1 to 8) is monitored by an Analog Front-End (AFE) module, which is connected to a Microcontroller Unit (MCU). These sections help monitor voltages across each cell to ensure they are within safe operating limits. Thermistors are included for temperature monitoring, which is crucial for preventing overheating.
Regulator and ADC: Each module has a regulator for power management and an Analog-to-Digital Converter (ADC) to convert the analog signals from the temperatures into digital form for processing by the MCU.
MCU and CAN Controller: The MCU processes the digital data from the ADCs and communicates with other components through the Controller Area Network (CAN). This setup enables communication between the BMS and other vehicle systems, ensuring coordinated operation.
Interconnects and Drivers: Various interconnects (like SPI) and driver integrated circuits (ICs) such as the HVIL driver IC, relay driver IC, FAN driver IC, and PUMP driver IC manage connections and operations of external devices like switches, relays, fans, and pumps, which are essential for maintaining optimal operating conditions within the battery pack.
Voltage and Current Regulation: Multiple voltage dividers and reference voltage circuits ensure stable operation. There is also a main regulator and related circuitry to maintain consistent voltage levels and supply power to connected loads.
Safety Features: Relays and a Manual Service Disconnect (MSD) provide critical safety functions to manually disconnect the battery pack in case of emergency or for service.
BMS Functions and Safety
Protecting the battery cells: The BMS shields the battery cells from damage in cases of abuse or failure. Protection is crucial to prevent disastrous consequences like fires or explosions. The BMS must identify issues such as overcurrent, overvoltage, or undervoltage, and react by shutting down the device or restricting the current flow to the cells.
Ensuring safety and extending battery life: A well-designed BMS protects battery packs from overcharging, over-discharging, overcurrent, short circuits, and extreme temperatures. It maintains safe operating conditions by continuously monitoring battery parameters and taking corrective actions. Additionally, the BMS extends the battery’s lifespan during regular use by regulating charge and discharge rates, monitoring temperature, and keeping the cells within their ideal operating range.
Diagnosing battery health: The BMS diagnoses battery health and performance through abuse detection, state-of-health (SOH) estimation, and state-of-life (SOL) estimation. Abuse detection identifies and prevents behaviors that could damage the battery pack, while SOH and SOL estimations provide critical information on the battery pack’s remaining capacity, expected cycle life, and end-of-life.
Maintaining functionality: The BMS is responsible for preserving the battery’s functional state, ensuring it is charged and discharged according to application requirements and remains within the optimal operating range. It optimizes battery pack performance through State of Charge (SOC) estimation, power-limit computation, and cell balancing. Accurate SOC estimation uses algorithms like a combination of coulomb counting, voltage-based estimation, and Kalman filtering. Power-limit computation prevents high power output from causing safety hazards or damaging the battery pack. Cell balancing ensures equal charge across all cells using passive, active, or hybrid balancing methods.
Supplying relevant information: The BMS must provide the application controller with the required information to maximize the battery pack’s current usage. This might involve setting power limits, managing the charger, and offering other data to optimize battery performance. By fulfilling these responsibilities, The BMS ensures that battery-powered devices are safe, reliable, and efficient.
Acting as an interface: The BMS also acts as an interface between the battery pack and the rest of the system, enabling range estimation, communication, data recording, and reporting. Range estimation calculates the remaining range based on SOC and other parameters. Communication protocols, like CAN bus, LIN bus, or Ethernet, allow host applications to receive real-time information about the battery pack’s status. Data recording and reporting help monitor the battery pack’s performance and identify potential issues.
Integrating systems: The BMS is interconnected with all battery pack components and the host-application control computer, ensuring the battery system’s safety, performance, and maintenance.
Summary
The Battery Management System (BMS) plays a pivotal role in battery performance, safety, and maintenance. The importance of these factors and the BMS’s functionality remain unchanged. The BMS safeguards battery cells from damage, optimizes safety, and extends battery life by managing operational conditions and detecting potential abuses. It also diagnoses battery health, maintains functionality through SOC estimation and cell balancing, provides essential data to application controllers, acts as an interface for system communication, and integrates with all battery components.
The BMS will continue to evolve as its requirements become more thorough and sophisticated.
