Study On Internal Short Circuit Fault Diagnosis And Thermal Runaway Safety Warning Of Lithium-Ion Battery Packs

To counteract the global energy crisis and environmental pollution,transportation electrification is considered an important measure in energy reform.Electric vehicles have ushered in large-scale rapid development,as an important part of transportation electrification.However,as a key energy storage component of electric vehicles,power batteries are at risk of faults due to its own inherent defects,complex working conditions and abuse of operation.Battery faults will lead to accelerated deterioration of battery performance and thermal runaway in severe cases,which will bring huge hidden dangers to the safety of electric vehicles.Internal short circuit fault is the main cause of battery thermal runaway.Therefore,it is necessary to study accurate and effective internal short circuit fault diagnosis and thermal runaway safety warning algorithm for lithium-ion battery packs in electric vehicles.This paper takes lithium-ion battery pack as the research object.Aiming at the internal short circuit fault,the electro-thermal characteristics are studied,and the diagnosis method of the early internal short circuit fault is proposed.Aiming at the thermal runaway problem,a thermal runaway safety warning method applied to the actual vehicle operation scenario is proposed.The specific research work of this paper is as follows:Firstly,the causes and development evolution process of internal short circuit fault in lithium-ion batteries are summarized,and the electro-thermal characteristics of early internal short circuit fault of batteries are preliminarily determined.The short circuit model of soft-package lithium-ion battery pack is jointly built by commercial simulation software Auto Lion and Matlab/Simulink,and multiple groups of simulation tests are designed to obtain the data set of internal short circuit fault.Based on the data set,the electrical characteristics of the early internal short circuit fault in batteries are further analyzed in detail,which can provide theoretical basis and data validation for the early internal short circuit fault diagnosis.Secondly,the capacity increment curve is used to extract fault features as the input of local outlier factor algorithm to realize the diagnosis of the early internal short circuit fault in lithium-ion battery packs.Compared with the voltage variation,the extracted features can easily identify the small changes in battery parameters,which makes the diagnosis more reliable.The Simulation data set and real vehicle fault data are used to verify the effectiveness of the proposed method.The results show that the proposed method can effectively identify the internal short circuit fault of the battery at the early stage,accurately locate the faulty cells in the battery pack,and quantitatively describe the severity of the fault.Finally,for the actual operation scenario of electric vehicles,the thermal runaway safety warning method of lithium-ion battery pack is proposed combining the state representation method and the cumulative sum method.The state representation method is used to calculate the state of each cell in the battery pack,and the cumulative sum method is used to evaluate whether the battery state is abnormal.Then the effectiveness,reliability and robustness of the proposed method are fully verified by using a large amount of real-world vehicle data.The results show that the proposed method can give early warning 13 days in advance for the slow developing thermal runaway and 44 minutes in advance for the rapid death thermal runaway.For the whole real vehicle data set,the warning accuracy of the proposed method reaches 97.73%,and the reliability is high.In addition,satisfactory warning results can be achieved for several observation window lengths,so the proposed safety warning method has strong robustness.Therefore,in practical application,the length of observation window can be appropriately extended to reduce the computational load of the system.This method can provide a new idea for thermal runaway safety warning of lithium-ion battery packs.