Reliability Modeling Method for Lithium-ion Battery Packs Considering the Dependency of Cell Degradations Based on a Regression Model and Copulas

Abstract

Lithium-ion batteries are widely used as basic power supplies and storage units for large-scale electric drive products such as electric vehicles. Their reliability is directly related to the life and safe operation of the electric drive products. In fact, the cells have a dependent relationship with the degradation process and they affect the degradation rate of the entire battery pack, thereby affecting its reliability. At present, most research focuses on the reliability of battery packs and assumes that their cells are independent of each other, which may cause the reliability of the evaluation to deviate greatly from the actual level. In order to accurately assess the reliability of lithium-ion batteries, it is necessary to build a reliability model considering the dependency among cells for the overall degradation of lithium-ion battery packs. Therefore, in this study, based on a lithium-ion battery degradation test, the Wiener process is used to analyze the reliability of four basic configurations of lithium-ion battery packs. According to the degradation data of the battery packs, the Copula function is used to quantitatively describe the dependent relationship in the degradation process of a single battery, and the quantitative dependent relationship is combined with the reliability model to form a new reliability model. Finally, taking the battery system of Tesla S as an example, a feasible optimization method for battery pack design is provided based on the model constructed in this work.

A Comprehensive Review of Key Technologies for Enhancing the Reliability of Lithium-Ion Power Batteries

“…In order to assess the reliability of lithium-ion batteries more accurately, Wang et al [36] proposed a reliability model for the whole degradation of lithium-ion battery packs considering the inter-cell dependency. According to the general linear model structure, a linear model is established, which only considers the equation of the internal structural relationship of the battery pack, as follows:…”

“…SOP is the available power that the battery can provide or absorb from the vehicle powertrain over a period of time, which is defined as the product of the threshold current and the corresponding voltage. The expression is given below: (36) where SOP charge (t) denotes the SOP for charging at moment t; SOP discharge (t) represents the SOP of the discharge at moment t; P min and P max are the minimum and maximum cell power limits, respectively; ∆t denotes a particular time range; V(t + ∆t) is the sampled terminal voltage at the first (t + ∆t) moments; I charge min and I discharge max denote the minimum continuous charging current and the maximum continuous discharging current from moment t to moment (t + ∆t), respectively.…”

Multiscale Modelling Methodologies of Lithium-Ion Battery Aging: A Review of Most Recent Developments

“…Apart from the Monte Carlo method, Wang et al [109] use the wiener stochastic process coupled with the Copula function to analyze the reliability of a LIB pack and the dependency between its cells. Galatro et al [7] implemented a three-parameter nonhomogenous gamma process to model LIB aging while accounting for cell spreading.…”

Reliability Study of BEV Powertrain System and Its Components—A Case Study

“…In other studies [9,10], a multi-fault diagnostic method was proposed to improve the reliability of battery system operation; this method was further improved by adding a function to estimate the charging state of the battery pack [11]. In order to accurately assess the reliability of lithium-ion batteries, a reliability model considering the dependency among cells for the overall degradation of lithium-ion battery packs was built in [12]. Apart from these, the reliability of the stator and rotor components in permanent magnet synchronous motors for BEVs has been studied using a combined fault tree and Petri net approach [13,14].…”