Why do we need BMS?

Lithium-ion batteries have become the preferred choice for energy storage in a wide range of applications, from electric vehicles and portable electronics to stationary energy storage systems. However, the performance, safety, and lifespan of these batteries are highly dependent on the proper management of the battery system.

This is where a lithium-ion battery management system (BMS) comes in. A BMS is an electronic system that monitors and controls the performance of a lithium-ion battery pack. The primary function of a BMS is to prevent overcharging, overdischarging, and overheating of the battery, which can lead to safety hazards, reduced performance, and shortened battery lifespan.

A typical lithium-ion battery pack consists of multiple individual cells connected in series and parallel configurations. Each cell has a voltage range that should not be exceeded during charging or discharging. If any cell in the pack is overcharged or overdischarged, it can result in irreversible damage to the cell, leading to capacity loss, thermal runaway, or even a fire.

The BMS continuously monitors the voltage, temperature, and current of each cell and the entire battery pack. It uses this data to ensure that the charging and discharging operations remain within safe limits. For example, if the voltage of any cell exceeds the upper limit during charging, the BMS will reduce the charging current to prevent overcharging. Similarly, if the voltage of any cell drops below the lower limit during discharging, the BMS will stop the discharge to prevent overdischarging.

In addition to the basic safety functions, a BMS can also provide other features to optimize the performance and lifespan of the battery pack. For example, the BMS can balance the voltage of each cell to ensure that all cells have the same voltage level, which can improve the overall performance and lifespan of the pack. The BMS can also calculate the state of charge (SOC) and state of health (SOH) of the battery pack based on the voltage, current, and temperature data, which can provide accurate information on the remaining capacity and expected lifespan of the pack.

Another important feature of a BMS is the ability to communicate with other systems and devices in the application. For example, a BMS in an electric vehicle can communicate with the vehicle’s motor controller to optimize the power delivery based on the battery’s SOC and temperature. The BMS can also communicate with the vehicle’s charging system to manage the charging process and ensure that the battery is charged within safe limits.

In summary, a lithium-ion battery management system is an essential component of any lithium-ion battery pack. It provides critical safety functions to prevent overcharging, over-discharging, and overheating of the battery, while also optimizing the performance and lifespan of the pack. As the demand for lithium-ion batteries continues to grow in various applications, the role of the BMS in ensuring the safe and reliable operation of these batteries becomes increasingly important.

Functions of BMS

Cell Protection: Overvoltage Charging and Under-voltage Discharging Protection.

Energy Management: – It shows the State of Charge(SOC) and State of Health (SOH) of the battery.

Prevention of Charge imbalance occurred in the individual cells from the Battery pack module: A battery pack usually consists of several individual cells that work together in combination. As an ideal case, all the cells in a battery pack should be kept at the same state of charge. If the cells go out of balance, individual cells can get stressed and lead to premature charge termination and a reduction in the overall cycle life of the battery. 

Thermal Management: Lithium-ion batteries are designed to operate at specific temperature range (10^oC to 55^oC). Overheating causes liquid electrolyte in the cells to degrade, melting of polymer separator can cause internal short circuit etc. problems. Cooling below minimum temperature may cause very low ionic conductivity so battery will not work at all. So BMS must monitor temperatures at various part of battery pack and maintains the temperature in the pack.

Detection and Isolation of Faults: BMS should be able to detect and isolate the faults, it may be individual cell damage, short-circuit etc.