EV Power Battery System Test Knowledge – Part 1

In recent years, the level of national economic development has been improved, science and technology has achieved rapid development, and new energy technologies have been deeply researched and applied. For the purpose of green and sustainable development, more and more industries gradually developing in the direction of new energy Nowadays, new energy vehicles have gradually become an important direction of mobile production In the production process of this type of automobile, the most important part is the power battery system, which is the key part of the safe and stable operation of the automobile.


Energy security and environmental crises are becoming increasingly severe, and countries around the world are taking diversified measures to reduce harmful pollutant emissions and energy consumption. Actively developing new energy vehicles, with electric and hybrid vehicles as representatives, has become an international consensus and one of China’s important strategies.


Lithium ion is widely used in the fields of new energy vehicles and energy storage power plants, with its advantages mainly being high energy density, high power density, and long service life. With the rapid development of new energy vehicles, the number of reported fire accidents has increased in recent years, indicating that the proportion of new energy vehicle accidents caused by power battery issues is relatively high. This type of battery failure mainly refers to overcharging, discharging, and overheating, which can cause the internal temperature and pressure values of the battery pack to rise, causing the battery system to lose control.


To avoid new energy vehicle safety accidents, relevant researchers are currently implementing comprehensive battery fault diagnosis and safety management work from both the onboard and cloud platforms. In the past, the on-board battery management system used to assess the actual charging and health status of the battery pack by detecting its voltage and current parameters, in order to ensure the safety of the power battery. However, due to the limitations of BMS during the process, the safety warning strategy was relatively simple and could not control the safety of the battery system in real-time.


To solve the above problems, it is necessary to attach importance to remote platform fault diagnosis and early warning technology. With the help of on-board terminals, power battery system data can be transmitted to the new energy vehicle big data cloud platform, and power battery fault diagnosis methods can be comprehensively analyzed by uncovering massive data.


1 Power Battery Management System

In the field of new energy vehicles, the power battery management system has two main functions: one is to monitor battery performance parameters in real time. And the other is to effectively control the battery temperature based on the application environment to prevent the battery temperature value from being too high or too low, which will affect the battery life and performance.

During the process, a malfunction occurs in the battery management system, which limits the above functions and prevents effective prediction of battery compliance issues. This can cause the battery to lose effective control, damage the battery, and in severe cases, cause vehicle driving failures, posing a threat to people’s life and property safety.


2 Internal Fault Analysis


2.1 Overcharging issues

Vehicle power sources effectively meet voltage and capacity requirements. The power battery system is composed of single batteries connected in series or in parallel. However, due to manufacturing defects and differences in working conditions, single batteries often encounter inconsistencies.

During the vehicle charging process, charger failure or inaccurate detection and estimation of battery status by the management system can cause overcharging problems in some individual batteries.

The total voltage value of the battery system far exceeds its upper limit value, and some individual batteries may still experience overcharging. Overcharging lithium-ion batteries can cause internal electrochemical reactions and loss of active substances, increase the temperature value of the battery pack, accumulate gas, and cause battery explosion.


2.2 Overdischarge issues

In general, setting the discharge cut-off voltage is used to avoid over discharge faults. However, due to the high current impact, unreasonable design of the power battery management system, and relatively long battery storage time, these fault factors are still common problems in the application stage of electric vehicles.


During the over discharge process, the lithium ion extraction ability in the negative electrode state will decrease, while the polarization voltage of the battery will increase. The negative electrode copper collector will become copper ions under oxidation and gradually dissolve in the electrolyte. This phenomenon will increase the self discharge rate value of the power battery. This over discharge behavior will not directly cause thermal runaway problems, but will cause loss of capacity or changes in thermal stability, The impact on the tolerance of power battery abuse conditions can cause dangerous accidents during recharging or use.


2.3 Overheating issues

Power batteries, whether charged or discharged, will face intense electronic motion, which can generate thermal effects. In most cases, abnormal heating of the battery can occur, and side reactions, external short circuits, and internal short circuits can occur during charging and over discharging. Based on the background of high temperature conditions, lithium-ion batteries will experience a certain degree of expansion, impedance growth, and shortened cycling time.


During the high rate charging cycle, heat will continue to accumulate in the battery, causing the temperature value to gradually increase and increasing the risk of thermal runaway. Overheating of the battery will shorten the degradation time of the positive material, and the facial mask of the negative solid electrolyte will appear, resulting in a very obvious capacity loss. Some gases will appear during the decomposition of the internal materials of the lithium ion battery. When the pressure value rises, the battery will expand and face the risk of explosion.

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