Batteries are used extensively in a variety of applications, including your phone, emergency light, and automotive. Users can monitor individual cells within a battery pack using a battery management system. It is critical to maintain stability throughout the pack as cells work together to release energy to the load.
This is where a battery management system (BMS) comes into play. A BMS enables continuous monitoring, data collection, and communication to an external interface so users can see the state of each cell and the battery pack’s overall health. A battery pack’s BMS monitors and regulates it in order to protect it from harm, extend its life, and keep it running within its safety limits. This article discusses the battery management system, its operating concept, and many other topics.
What Is A BMS (Battery Management System)?
The Brain of a battery pack is said to be the Battery Management System (BMS). The BMS is a system of electronics that monitors and controls the operation of the battery. Most significantly, it prevents the battery from exceeding its safety limits. A Battery Management System, or BMS, monitors and changes internal operational parameters such as temperature, voltage, and current as the battery is charging and discharging. The BMS calculates the battery’s SoC (State of Charge) and SoH (State of Heat) to improve battery safety and performance (State of Health).
It guards against overcharging or discharging the battery pack. This keeps the charge level within the maximum and minimum authorized limits, preventing unexpected accidents [explosions]. As a result, a BMS is critical equipment for assuring the safety of both the battery and the user. It prevents the battery pack from being overcharged or discharged. This prevents abrupt mishaps [explosions] by keeping the charge level within the maximum and minimum permissible capacities.
Battery management system (BMS) is a technology designed to the oversight of a battery pack, which is an assembly of battery cells, electrically organized in a row x column matrix configuration to enable delivery of targeted range of voltage and current for a duration of time against expected load scenarios. The oversight that a BMS provides usually includes:
- Monitoring the battery
- Providing battery protection
- Estimating the battery’s operational state
- Continually optimizing battery performance
- Reporting operational status to external devices
What is the Function of a Battery Management System?
The BMS’ principal purpose is to prevent the battery cells from harm caused by overcharging or discharging. In addition, the BMS calculates the remaining charge, monitors the battery’s temperature, and checks for loose connections and internal shorts to ensure the battery’s health and safety.
The BMS also balances the charge throughout the cells to ensure that each cell operates at its full potential. The BMS shuts down the battery to protect the lithium-ion cells and the user if it detects any harmful conditions.
Building Blocks of Battery Management System
The BMS board’s design is a little tricky. We’ve outlined the building components of the BMS briefly.
Integrated circuits for battery management come in a variety of shapes and sizes. From a simple analogue front-end with balancing and monitoring that requires a microcontroller (MCU) to a self-contained, fully integrated system, the functional components are grouped in a variety of ways. Let’s take a look at the function and technology of each block, as well as the benefits and drawbacks.
There are four main functional blocks,
- Cut-off FETs
- Fuel Gauge Monitor
- Cell voltage monitor
- Temperature Monitor
Between the battery and the charger, a FET-driver serves as an isolation device. It is used to connect the battery pack’s high and low sides.
- High-side – Activates NMOSFET using the charge pump driver
- Low-side – Activates NMOSFET without charge pump driver
The BMS’s overall cost is reduced because of the incorporated Cut-off FETs. It also eliminates the use of high-voltage components, which might take up a lot of space on the die.
Fuel Gauge Monitor
This aids in the tracking of charge as it enters and exits the battery pack. Multiplying current and time yields the amount of charge flowing. Although numerous ways are utilized to monitor current flow, the most efficient and cost-effective solution is to employ a 16-bit ADC with low offset and high common-mode rating to measure the voltage of the sense resistor. Higher ADC is advantageous for obtaining a wider dynamic range at a faster rate.
Cell Voltage Sensors
The monitoring of cell voltage is a typical feature of the Battery Management System. It’s useful for determining the battery’s health. For safety and improved lifetime, all cells in a battery should operate at standard voltage levels during charging and discharging. Check out this blog Series Parallel Configuration of Lithium Batteries to learn how battery packs are made by connecting battery cells in series and parallel.
As technology is evolving, batteries are made to supply high currents in the meantime keeping the voltage constant. Temperature sensors monitor each cell in an energy storage system (ESS) or a cluster of cells for smaller and more portable applications. To monitor the temperature of each circuit, thermistors with an inbuilt ADC voltage reference are commonly utilised. The internal voltage reference is used to reduce temperature reading inaccuracies caused by environmental temperature variations.
This feature is useful since it will notify you to start/stop charging or discharging if the temperature increases beyond the rated value.
Other Building Blocks
Few more of the available blocks are,
- Battery Authentication – prevents the connection of BMS electronics to the third-party battery pack.
- Real-time Clock (RTC) – used in black-box application
- Memory – used in black-box application
- Daisy Chain – simplifies the connection between stacked devices
How Does a Battery Management System Work?
Individual cells in the battery pack are monitored by the battery management system. It then estimates how much current may safely enter (charge) and exit (discharge) the battery without causing damage. The computer in the BMS continuously checks the cell voltage and current and adjusts the MOSFETs accordingly.
The current restrictions keep the battery from being overdrawn or overcharged by the source (typically a battery charger) and the load (such as an inverter). This protects the battery pack against excessively high or low cell voltages, extending the battery’s life.
The BMS only uses one bus for charging and discharging. Because both charging and discharging FETs are switched off, there is no current flow at first. The microcontroller in the BMS recognises the input voltage and triggers the charging MOSFET, which recharges the battery.If no voltage is available at the input pin, the BMS assumes the load is connected and activates the discharging FET. Normally two types of cell balancing are used in BMS.
- Passive cell balancing
- Active cell balancing.
Bypass resistors are used in passive cell balancing to discharge excess voltage and equalise with other cells. The excess charge of one cell is transferred to another cell with a low charge in the active cell balancing to balance the charges. Charge-storage capacitors and inductors are used.
Why is a BMS Important?
Battery management systems are essential for preserving the health and longevity of the battery, but they are much more crucial from a safety standpoint. Lithium-ion batteries’ liquid electrolyte is extremely flammable. To avoid a fire, these batteries must always be performing at their best and within acceptable limits.
A battery management system (BMS) can protect its battery by keeping it from running outside of its safe operating range.
- Over-current (may be different in charging and discharging modes)
- Over-voltage (during charging), especially important for lead–acid and Li-ion cells
- Under-voltage (during discharging)
- Over-pressure (NiMH batteries)
- Ground fault or leakage current detection (system monitoring that the high voltage battery is electrically disconnected from any conductive object touchable to use like vehicle body)
The BMS may prevent operation outside the battery’s safe operating area by:
- Including an internal switch (such as a relay or solid state device) which is opened if the battery is operated outside its safe operating area
- Requesting the devices to which the battery is connected to reduce or even terminate using the battery.
- Actively controlling the environment, such as through heaters, fans, air conditioning or liquid cooling
The Benefits of Battery Management Systems
. The benefits of BMSs can be summarized as follows.
- Functional Safety:
The term “functional safety” refers to the ability to do This is, without a doubt, very prudent and necessary for big format lithium-ion battery packs. Even smaller formats, like as those found in laptops, have been known to catch fire and inflict significant damage. The personal safety of users of goods that employ lithium-ion batteries leaves minimal opportunity for error in battery management.
- Life Span and Reliability:
The electrical and thermal protection management of the battery pack guarantees that all cells are utilised within the defined SOA requirements. This careful attention guarantees that the cells are protected from abusive use and rapid charging and discharging cycling, resulting in a stable system that can possibly give many years of dependable service.
- Performance and Range:
Cell-to-cell balancing is used in BMS battery pack capacity management to equalise the SOC of adjacent cells across the pack assembly, allowing for maximum battery capacity. A battery pack could eventually become worthless without this BMS feature to account for differences in self-discharge, charge/discharge cycling, temperature impacts, and general aging
- Diagnostics, Data Collection, and External Communication:
Continuous monitoring of all battery cells is one of the oversight jobs, and data logging can be used for diagnostics on its own, but it is commonly utilised to compute the SOC of all cells in the assembly. This data is used for balancing algorithms, but it can also be used to tell external devices and displays about the available energy, estimate expected range or range/lifetime depending on current usage, and offer information about the battery pack’s condition.
- Cost and Warranty Reduction:
The addition of a BMS to a BESS raises expenses, because battery packs are costly and possibly dangerous. The more complex the system, the higher the safety requirements, necessitating the presence of a BMS supervisor. However, protecting and maintaining a BMS in terms of functional safety, lifespan and durability, performance and range, diagnostics, and other factors ensures that overall costs, including warranty costs, will be reduced.
The popularity and design of a BMS is steadily increasing as lithium-ion batteries become more common in automobiles. Knowing about this technology is becoming increasingly vital. To summarise, battery management systems can be created with a variety of functional blocks and design techniques. Careful study of battery needs and battery life goals will define the right architecture, functional blocks, and associated ICs to create your battery management system and charging scheme to improve battery life.