Current Variation in Parallelized Energy Storage Systems

Abstract

Abstract-an electric vehicle battery pack may employ cells connected electrically in parallel to meet energy and power requirements. For the battery management system, cells connected in parallel are often treated as a single larger component. However, research has identified that the state of charge and cell current may not be equal due to differences in capacity, impedance and cell temperature. In this paper, the authors develop a parallel cell model validated against experimental data. The model is used to evaluate cell energy variation and the impact this can have on the design of highly parallelized battery systems.

Identification and quantification of ageing mechanisms in Lithium-ion batteries using the EIS technique

“…This definition is in agreement with several authors [21] - [25] and procedures [26], [27]. Undertaking the experimental investigation described in [11], each cell was aged initially by 0, 50, 100 and 150 cycles respectively before being connected in parallel to emulate an SoH imbalanced scenario. For simplicity this work is only focused on analysing the ageing mechanisms of the least aged cell.…”

“…EIS results are usually represented by the inverse of Nyquist plots, which relates the imaginary (y-axis) and the real (x-axis) part of the impedance. The BMS often defines the internal impedance of the battery as the turning point at low frequency of the EIS plot [11], [12]. Fitting the Nyquist plots to a LIB ECM allows the battery kinetic processes to be modeled as illustrated in Figure 1A) and B).…”

Energy Management of Parallel-Connected Cells in Electric Vehicles Based on Fuzzy Logic Control

“…Therefore, it is necessary to establish a PCCP model to investigate PCCP management. Some researchers [15,31] proposed a parallel-connected cell pack model on the assumption that all the batteries are the same, which is obviously impractical. Currently, most PCCP models donot consider thermal influence, thus making most models imprecise.This study utilized the first-order RC equivalent model to build a model of eight parallel-connected cell packs.…”

“…Many researchers have discussed cell inconsistency from different perspectives. Bruen et al [15] evaluated the variation in energy among cells and investigated its probable effect on the design of highly parallelized battery systems. Yang et al [1] introduced the influence of uneven temperature distribution on PCCP discharge characteristics and service life.…”

A Cell-in-the-Loop Approach to Systems Modelling and Simulation of Energy Storage Systems

“…Given that most commercial vehicle battery systems employ a topology using cells in both series and parallel, a further application of CILS would investigate a parallel connection of differentially aged cells. For cells having different values of impedance and capacity, initial research has already highlighted the differential current flow that is possible between adjacent current paths and the resulting impact that this has on system efficiency, ageing and safety [46]. In order to meet the potential end-user requirements introduced in Section 6.1, two primary challenges remain and are the subject of on-going research by the authors.…”