Lithium ion battery pack power fade fault identification based on Shannon entropy in electric vehicles

Fault diagnosis for inconsistent cells in a battery pack is important for electric vehicle (EV) safety. Discovering the fault and identifying its cause on-site are extremely challenging. The literature has rarely explored such issues. This paper presents a battery pack system in a demonstrated EV with 96 cells in series and discovers the battery power fade fault during the demonstration. The preliminary analysis, after collecting data and preprocessing the typical data periods, shows that the internal or contact resistance increase causes the fault. To further identify the fault cause, we introduce an equivalent circuit model (ECM) and identify the cell resistances using the total least squares algorithm. A diagnostic method is proposed, using the identified cell resistances from 3 months demonstration data. Calculating the Shannon entropy clearly identifies the cause of the power fade fault. Appropriate measures are taken to solve the fault, and the latent safety issue is eliminated. The proposed diagnostic method can be used on-site for EV diagnosis without laboratory testing methods.

► The battery power fade fault in EV is discovered during the demonstration.
► The internal or contact resistance increase causes the EV power fade.
► Cell resistance fault is attributed to contact resistance using Shannon entropy.
► Proposed diagnostic method can be used without laboratory testing methods.