| A large number of investigations show that the results of most of the electric car accidents like bursting into flames or explosion are caused by a serious security problem inside the battery pack.The security problem of battery packs is not often starting with unreliable design of a single performance or component,but after all the parts are integrated into a system.Because it becomes a complex assembly consists of multiple subsystems and works under the combination of the thermal environment,electric environment and mechanical environment at the same time,presents many characteristics like diversity,interactivity,evolving character,emergence and many other features.Its security is no longer a simple superposition of the security of each part.So its safety design,analysis and evaluation is a multidisciplinary,multi-objective integrated complex system problem.The existing safety research mainly focuses on the characteristics of one part of the battery pack or the reliability analysis and design of a certain component.The performance analysis and evaluation at the complex system level are not yet carried out.At the same time,the battery pack manufacturers still lack a set of applicable theoretical system and scientific,standardized process approach to guide its development currently.Based on the characteristics of cognitive complex system,a set of PDEO method(P for performance requirement analysis,D for product development,E for performance evaluation and O for product optimization),which is a method combined with the relevant theory to analyze and evaluate the safety performance of battery pack,is proposed in this paper.This method is used to analyze the dynamic response of an external structure and internal connection of a case under random excitation and to optimize the structure based on safety evaluation.In the module P,after the study about the effects of random vibration,the initial connection state of the electrical contact and the discharge current on the discharge characteristics and heat generation of the battery module,the necessity of the study of the internal contact dynamic environment of the battery pack is proposed.In the module D,based on the battery's equivalent mechanical model and consideration of the actual contact assembly conditions,the battery pack refinement dynamics modeling method is established.Combining with a battery pack development example,the sub-models are established and tested.The optimal contact parameters are determined by the optimization algorithm.Compared with the results of madal analysis of the centralized quality model,the connection simplified model and the contact considering model,the accuracy of the contact model is verified,and also the validity of the modeling method.The stress and acceleration of external structure and internal critical electrical contact point under steady-state random vibration and transient shock are obtained.It is found that the dynamic response of the contacts at different positions is very different and shows a strong non-uniformity even under the same vibration condition.In the module E,the evaluation index and method of the vibration safety of the battery pack are put forward by using the entropy weight method.In the module O,taking the double target of vibration safety and light weight as an example,the example battery pack was optimized by using the evaluation method.Through the thickness optimization,the weight of original steel battery pack decreased by 3.97% without decreasing the vibration safety requirement.By trying to use high-strength lightweight materials PDCPD and 6009 Al-6009 alloy,the weight decreased by 7.28% with superior vibration safety maintained.Complex system thinking for battery pack,"PDEO" method,dynamic analysis results and the evaluation system provide references for positive design,productive development and security analysis of the battery pack... |
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