What Is a Battery Management System and How Does BMS Work?

Battery Management System, or BMS, is an essential component in modern-day electric vehicles (EVs) and other battery-powered systems. It plays a critical role in ensuring that the battery operates safely and efficiently, and helps to extend the battery’s lifespan. In this article, we will discuss how BMS works and its importance in the world of EVs and Emergency mobile EV charging system.

What is a BMS?

A BMS is an electronic system that manages and monitors the performance of a battery pack. It performs several functions, including monitoring the state of charge, managing the charging and discharging process, and protecting the battery from damage.

The BMS typically consists of several components, including a microcontroller, sensors, and communication interfaces. The microcontroller is the brain of the system and is responsible for monitoring the battery’s performance and controlling its operations.

The sensors in the BMS are used to measure various parameters, such as the battery’s voltage, current, and temperature. The communication interfaces allow the BMS to communicate with other systems, such as the EV’s motor control unit or a charging station.

How does a BMS work?

The BMS works by monitoring the battery’s performance and controlling its operations to ensure that it operates safely and efficiently. It uses several algorithms and techniques to achieve this, including state of charge estimation, cell balancing, and temperature monitoring.

State of charge estimation

The state of charge (SOC) is the amount of energy stored in the battery at a particular time. The BMS uses several techniques to estimate the SOC accurately, including voltage-based methods, current-based methods, and model-based methods.

Voltage-based methods use the battery’s open-circuit voltage (OCV) to estimate the SOC. The OCV is the voltage measured across the battery terminals when it is not connected to any load. The BMS uses a lookup table to correlate the OCV with the SOC.

Current-based methods use the battery’s current flow to estimate the SOC. The BMS measures the current flowing in and out of the battery and uses an integration algorithm to calculate the SOC.

Model-based methods use mathematical models of the battery’s behavior to estimate the SOC. These models take into account various factors, such as the battery’s chemistry, temperature, and aging.

Cell balancing

Cell balancing is the process of ensuring that all the cells in a battery pack have the same state of charge. Cell balancing is essential because if one cell has a lower state of charge than the others, it can cause that cell to over-discharge, leading to permanent damage.

The BMS uses several techniques to balance the cells, including passive balancing, active balancing, and hybrid balancing. Passive balancing is the simplest form of balancing and involves the use of resistors to discharge the cells with a higher state of charge. This method is less efficient but is less expensive. Active balancing is a more advanced form of balancing and involves the use of a circuit that can transfer charge between the cells. This method is more efficient but is more expensive. Hybrid balancing is a combination of passive and active balancing and involves the use of both methods to balance the cells.

Temperature monitoring

Temperature monitoring is essential because high temperatures can damage the battery and reduce its lifespan. The BMS monitors the battery’s temperature and takes appropriate action to ensure that it stays within a safe operating range.

The BMS uses several techniques to monitor the temperature, including thermistors, infrared sensors, and internal temperature sensors.

Performance diagram of BMS in EMEVCS

The Battery Management System used in the Emergency mobile EV charging system was developed specifically for high-voltage battery storage systems and performed excellently. The distributed architecture and modular design make it easy to assemble and maintain.