With the increasing number of electric vehicles, in addition to seeking batteries with high energy density and high safety, the importance of battery energy management systems is also increasing. Different power batteries have different properties, and even batteries of the same type have inconsistencies in their properties, which may increase the risk of accidents during use. Therefore, it is very important to effectively manage the power battery system to ensure the safety of electric vehicles. It is also necessary to ensure the performance of the battery system, extend battery life, and improve battery efficiency.

　　Battery management system composition and principle

　　The battery management system (BMS), also known as Battery Management System, determines the status of the entire battery system by detecting the status of each single cell in the battery pack, and makes corresponding control adjustments and strategy implementation for the power battery system based on their status to achieve power management. The charge and discharge management of the battery system and each cell ensures the safe and stable operation of the power battery system.

　　A typical battery management system topology diagram

　　A typical battery management system topology structure is mainly divided into two major blocks: the master control module and the slave control module. Specifically, it consists of a central processing unit (main control module), data acquisition module, data detection module, display unit module, control components (fuse device, relay), etc. Generally, data information communication between modules is achieved by using internal CAN bus technology.

　　Based on the functions of each module, BMS can detect the voltage, current, temperature and other parameters of the power battery in real time, implement thermal management, balance management, high voltage and insulation detection of the power battery, and calculate the remaining capacity, charge and discharge power of the power battery, and SOC&SOH status.

　　Basic functions of the battery management system

　　The basic functions of the battery management system can be divided into three major parts: detection, management, and protection. Specifically, it includes functions such as data collection, status monitoring, equalization control, thermal management, and safety protection.

　　(1) Data collection

　　As the basis and premise for other functions in the battery management system, the accuracy and speed of data collection can reflect the quality of the battery management system. Other functions of the management system, such as SOC status analysis, balance management, thermal management functions, etc., are all analyzed and processed based on the collected data.

　　The objects of data collection are generally voltage, current, and temperature. In actual use, the electrochemical properties of the battery are different at different temperatures, resulting in different energy released by the battery. Lithium-ion power batteries are sensitive to voltage and temperature, so the effect of temperature must be considered when evaluating the battery's SOC.

　　(2) Status analysis

　　The analysis of battery status mainly includes two aspects: battery remaining power and battery aging degree, namely SOC evaluation and SOH evaluation. SOC allows drivers to obtain direct information and understand the impact of remaining power on cruising range. Much of the research at this stage focuses on SOC analysis and continuously enhances its accuracy. The analysis of SOC will be affected by SOH. The SOH of the battery is continuously affected by temperature, current, etc. during use and needs to be continuously analyzed to ensure the accuracy of SOC analysis.

　　In the analysis of SOC, there are mainly charge measurement method, open circuit voltage method, Kalman filter method, artificial neural network algorithm and fuzzy logic method. Here we briefly introduce the two methods of charge measurement method and open circuit voltage method.

　　(1) Charge measurement method

　　The charge measurement method calculates SOC by counting the charges charged and discharged from the battery over a period of time, that is, the accumulation of current over time. Although it is the most commonly used measurement method, it is affected by many factors, including data collection accuracy, self-discharge issues, etc. For example, due to the insufficient accuracy of the current sensor, there is an error between the current used for integral calculation and the real value, making the SOC result more and more biased. Therefore, when using the charge measurement method, some correction algorithms need to be used to correct various influencing factors and reduce the errors in calculation and analysis results.

　　(2) Open circuit voltage method

　　The open circuit voltage method is to calculate the SOC of the battery by measuring the open circuit voltage of the battery when the battery is in a static state. However, it should be noted that when using the open circuit voltage method, it is generally believed that SOC and electromotive force have a certain linear relationship, and any SOC value only corresponds to one electromotive force value. When using the open circuit voltage method, the voltage rebound effect must be taken into account. When the voltage does not rebound to a stable value, the calculated SOC will be too small. Compared with the charge measurement method, the open circuit voltage method cannot be used when the battery is working normally. This is its biggest problem.

　　There are great difficulties in measuring SOC very accurately during the implementation phase. For example, inaccuracies in sampling data caused by sensor accuracy and electromagnetic interference cause deviations in state analysis. In addition, battery inconsistency, historical data, and ambiguity in usage conditions also have a great impact on the calculation of SOC.

Read recommendations:

LR20

Introduction to Negative Electrode Free Batteries.rechargeable battery 18650 3.7v

Waterproof Rating of Waterproof Lithium Batteries

3.2v lithium battery

no 5 alkaline battery