What is a Battery Management System? – BMS Building Blocks, Working & Functions

Components of Battery Management System

Battery Monitoring Unit (BMU)

BMU is a fundamental component of BMS which helps to track health and performance of each cell within the battery pack. It monitors voltage and temperature of each individual cell, tracks batteries in and out current flow. Accurate monitoring by BMU prevents battery from overcharge, and deep discharge. 

Control Unit/Microcontroller

Control unit comprising a microcontroller acts as the brain of BMS and contributes to analyze, process, and execute data from various sensors. CU communicates with other components and external systems to ensure smooth battery operation.

It executes software algorithms by coordinating the operations of the Battery Monitoring Unit (BMU), temperature sensors, current sensors, and MOSFETs, the Microcontroller ensures that the overall system functions correctly and efficiently.

Balancing Circuit

Balancing circuit maintains the uniformity of charge levels among the cells by transferring energy from high-charged cells to low-charged cells. Two balancing techniques are employed in the Battery Management System.

Passive Cell Balancing

This method employs bypass resistors to discharge excess voltage from cells and equalize their charge levels.

Active Cell Balancing

In this approach, the excess charge from one cell is transferred to another cell with a lower charge to equalize them. It utilizes charge-storing capacitors and inductors.

By employing these cell balancing techniques, the BMS ensures that all cells operate within safe and optimal voltage ranges, enhancing overall battery performance and longevity.

Temperature Sensors

Temperature sensors monitor and provide real time temperature data of individuals and cells pack as whole. It triggers protective actions like reducing charging current, activating the cooling system of BMS. 

MOSFET 

Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFET) are semiconductor devices that play a crucial role in managing the power flow to and from the battery pack. MOSFETs function as electronic switches, enabling or disabling the connection between the battery and the load or charger. Its ability to precisely control power flow contributes significantly to the overall safety and efficiency of the BMS.

Data Logger

Data logger records and stores performance data from BMS over time. It provides helpful data that can be used to understand battery performance, planning maintenance.

Primary Functional Blocks of BMS

Cut-off FETs

Cut-off FETs

The Cut-off FETs serve as an isolation mechanism between the battery and the charger. They facilitate the connection of the high-side and low-side of the battery pack. The high-side activates the MOSFET using the charge pump driver, while the low-side activates the MOSFET without the need for a charge pump driver. Integrating Cut-off FETs reduces the overall cost of the BMS and eliminates the use of high voltage devices, thus saving significant die area.

Fuel Gauge Monitor

The Fuel Gauge Monitor aids in tracking the charge entering and leaving the battery pack. The charge flow is calculated by multiplying the current and time. Various methods can be employed to measure current flow, but the most efficient and cost-effective approach involves measuring the voltage across a sense resistor using a 16-bit ADC with low offset and a high common-mode rating. Employing a higher ADC allows for a broader dynamic range and faster operation.

Cell Voltage Sensors

Cell voltage monitoring is a standard function of the Battery Management System. It helps determine the battery's health by ensuring that all cells in the battery operate at standard voltage levels during charging and discharging. This approach enhances safety and improves the battery's lifespan.

Temperature Monitoring

With advancing technology, batteries are designed to supply high currents while maintaining a constant voltage. However, high current flow can lead to rapid temperature increases, potentially resulting in accidental explosions. 

To prevent this, the BMS continuously monitors the battery's temperature and regulates it to the rated value. This feature is valuable as it alerts users to start/stop charging or discharging when the temperature exceeds the specified threshold.

Battery Authentication

Battery Authentication block ensures only authorized batteries are used within a system. This block is useful in applications like electric vehicles, where safety and performance are of major importance. It also enables secure transfer of sensitive data like state-of-charge (SOC) and state-of-health (SOH) between the battery pack and the BMS.

Real-time Clock (RTC)

The Real-time Clock (RTC) is an essential block within a BMS providing accurate timekeeping, which is crucial for time-stamping battery events and maintaining synchronized operations within the system. It helps in tracking the duration of battery operation, logging charge and discharge cycles.

Memory

Memory within a BMS stores data related to battery performance, system configuration, and historical logs. Two types of memory used in a BMS, volatile memory (such as RAM) and non-volatile memory (such as EEPROM or Flash). This data plays a crucial role in diagnostics, predictive maintenance, and performance optimization. 

Daisy Chain

The Daisy Chain configuration is a method used to connect multiple battery management modules within a large battery pack. In a daisy chain, modules are connected in series, allowing for streamlined communication and control across the entire battery pack. This chain setup reduces wiring complexity and ensures that all modules can communicate with the central BMS controller efficiently. 

How Battery Management System Works

A Battery Management System (BMS) works continuously to monitor and manage the battery's state to prevent damage and optimize performance. BMU and temperature sensors constantly measure real-time parameters like cell voltage, current, and temperature. This data is essential for assessing the battery's state and ensuring safe operation.

Microcontrollers receive and process the data from the BMU and temperature sensors to assess the battery's state of charge (SOC), state of health (SOH), and remaining useful life based on the collected data.

The BMS works by constantly monitoring the battery's state and taking steps to protect it from damage. For example, if the battery's voltage gets too high, the BMS will shut off the charger. If the battery's temperature gets too high, the BMS will reduce the charging current.

The BMS also collects data about the battery's performance, such as its state of charge (SOC), state of health (SOH), and remaining useful life. This data can be used to optimize the battery's performance and extend its lifespan. The operation of a battery management system (BMS) relies on the complexity of the onboard electronic components.

The BMS's microcontroller constantly measures the real-time cell voltage and current, using this information to control the switching of MOSFETs. The BMS employs a single bus for both charging and discharging operations.

Initially, both the charging and discharging FETs remain off, resulting in no current flow. The BMS's microcontroller detects the voltage at the input and activates the charging MOSFET, initiating the battery charging process.

If there is no voltage present at the input pin, the BMS determines that a load is connected and activates the discharging FET.

Types of Battery management Systems

Balancing the charge between battery cells is crucial for maintaining the health and performance of battery packs. Different balancing techniques offer unique advantages and challenges. On the basis of balancing technique BMS can be categorized in 3 categories like Passive BMS, Active BMS and Hybrid BMS. 

Passive BMS

Passive battery management system is a cost effective option of BMS where excess energy in overcharged cells is discharged as heat. This type of BMS is suitable for a battery system having minimal voltage difference between the cells of the battery cells pack.

Active BMS

Active BMS is an advanced system with additional components as mentioned above in the blog post like Microcontroller, BMU, Sensors. These additional electronic components help to monitor and redistribute the energy among the cells to maintain uniform voltage levels across the battery pack. This method is beneficial for Li-ion battery systems where there are significant voltage difference cells.

Hybrid BMS

Hybrid Battery management system combines the positives of active and passive BMS to offer balanced solutions. Hybrid BMS pays attention to enhancing cell life and performance of the battery without surging the costing of BMS. 

Beyond this there are different types of BMS based on battery chemistry, system integration, balancing techniques, scalability & flexibility, and communication protocol. 

Importance and Benefits of BMS

Safety

Thermal management function of BMS protects the battery from overcharging that can lead to fire or explosions. Advanced BMS is capable of detecting and isolating short circuits preventing battery damage which is crucial for safety and reliability of the battery system.

Extended Life

Cell balancing features of BMS ensure even charging and discharging among the cells and prevent overload on weaker cells. Charging control unit ensures an optimized charging cycle preventing it from overcharging and degrading of battery cells.

Improved Performance

Accurate State of charge(SoC) reading allows users to make informed decisions about the battery usage improving overall performance of the battery.

Reduce Maintenance Cost 

Early problem detection by BMS systems allow timely maintenance and replacement of faulty components. By protecting the battery from extreme conditions BMS reduces wear and tear of components and longer service life for the battery. 

BMS Applications Across Industries

Electric Vehicles (EVs)

Battery Management System is crucial in EVs for ensuring the health and efficiency of the vehicle's battery pack. BMS monitors various parameters such as voltage, current, and temperature to optimize performance and extend battery life. 

Renewable Energy Systems

Battery Management Systems play a vital role in renewable energy systems, particularly in energy storage systems (ESS) associated with solar and wind energy. 

Consumer Electronics

In consumer electronics, Battery Management Systems are essential for maintaining the performance and safety of devices like smartphones, laptops, and wearables. For portable and wearable devices, the BMS ensures that the battery remains efficient and reliable, which is crucial for maintaining the functionality and usability of these everyday gadgets.

Telecommunications

Telecommunications infrastructure relies heavily on reliable power sources, and BMS technology is crucial for managing battery systems in this sector. Uninterruptible Power Supplies (UPS) equipped with BMS ensure that telecom equipment remains operational during power outages or fluctuations. 

Medical Devices

Battery Management Systems are critical for ensuring the reliability and safety of battery-powered medical devices. Devices such as pacemakers, insulin pumps, and portable diagnostic tools depend on stable and long-lasting batteries. 

Aerospace and Defense

In aerospace and defense applications, the BMS oversees batteries used in avionics, emergency power supplies, and other essential systems, ensuring their reliability and safety. In military applications, BMS technology is employed to manage batteries in portable and vehicle-mounted equipment. 

Industrial Applications

Industrial environments use Battery Management Systems to manage batteries in electric-powered vehicles such as forklifts and Automated Guided Vehicles (AGVs). Additionally, in large-scale industrial energy storage systems, the BMS monitors and manages battery banks to provide reliable backup power and stabilize energy supply. 

Electric Grid and Power Systems

In the electric grid and power systems, Battery Management Systems are integral to managing grid-scale energy storage systems. These systems store excess energy generated from various sources, such as renewable energy, to be used when demand exceeds supply. 

FAQs on Battery Management System

How to Select the Right BMS?

Selecting the right Battery Management System (BMS) needs consideration of several factors, like type of battery, application requirements, and safety considerations. You may also need to consider features like cell balancing, thermal management, and communication interfaces. Assess the BMS's compatibility with your existing hardware and software, including the ability to interface with other system components. 

What are the challenges associated with BMS?

There are several challenges in designing a Battery Management System (BMS) like cell monitoring and controlling, managing heat presentation, ensuring efficient cell balancing. Other challenges in BMS are integrating BMS with other components without compromising reliability and efficiency. You may also find it challenging to mitigate faults like overcharging, and short circuits. 

Does a BMS improve the lifespan of a battery?

Yes BMS improves battery lifespan by preventing the over charge and discharge processes to ensure cells operate within safe limits. Also, cell balancing of BMS ensures that no single cell is overworked, which helps maintain the overall health of the battery and extends its life.

What are the common features to look for in a BMS?

When choosing a Battery Management System (BMS) consider features like cell balancing, overcharge and over-discharge protection to prevent damage, temperature monitoring, real-time data logging to track battery performance. You should also look if BMS has communication interfaces that allow the BMS to interact with other devices in the system that are crucial for advanced monitoring and control.

Can a BMS be upgraded or replaced?

Yes, a BMS can be upgraded or replaced, but it depends on the system’s design. Some BMSs are modular, allowing for easy upgrades as technology advances or as your power needs change. Replacing a BMS requires careful consideration to ensure compatibility with the existing battery pack and system components.

How does a BMS handle battery cell failures?

A BMS monitors each cell within the battery pack and can detect cell failures early. When it identifies a problematic cell, the BMS may isolate it to prevent it from affecting the rest of the battery pack. In some advanced systems, the BMS will adjust the operation of the remaining cells to compensate for the failed cell, maintaining overall system performance and safety.