Effect of Capacity Variation in Series-Connected Batteries on Aging

Abstract

Batteries are used in various combinations in various fields. Research on single-cell batteries is well underway and is approaching a stabilization phase. However, problems caused by battery combinations are still insufficiently studied. The purpose of this study was to investigate the cause of fires due to gradual damage in a large-capacity energy storage system (ESS). In the paper Energy Storage System Safety Operation Plan by Preventing Overcharge During Relaxation Time, which was based on the fact that most fires in large-capacity energy storage devices occurred during the diastolic period, it was proven that the inflow of compensation current due to a voltage imbalance in the cell was the cause. The total amount of compensation current is determined by the voltage deviation of the battery. Batteries connected in series have different rates of aging due to differences in their capacities. Thus, with use, the total amount of compensating current continues to increase until a fire occurs. In this study, by analyzing the effect of battery-capacity deviation on the aging of individual cells, it was confirmed that the capacity deviation increased as the battery was used, resulting in an increase in the total amount of compensation current. In addition, if a solution to the problem is presented and the proposed solution is applied, the allowable range of battery-capacity deviation will be widened. We used Matlab 2009a, assuming a real environment. Using Simulink, problems were identified through simulation, improvement measures were suggested, and the proposed method was verified via simulation.

Voltage Reference Realignment Cell Balance to Solve Overvoltage Caused by Gradual Damage of Series-Connected Batteries

“…In previous studies, a cell balancing method was proposed to make the SOC of all cells 100% when charging was complete [7]. However, this method can put a heavy burden on the BMS, as it requires the individual calculation of the SOC of all series-connected batteries.…”

“…Of course, the rate of aging proceeds differently [7,[30][31][32][33][34][35][36][37][38]. As this phenomenon is repeated, the aging of a battery with a relatively small capacity is accelerated.…”

“…Most of the battery fires of large-capacity Energy Storage Systems (ESSs) occurred during the dormant period. An electric vehicle fire case was studied in "Effect of Capacity Variation in Series-Connected Batteries on Aging" [7]. The case of a large-capacity ESS was studied in "Energy Storage System Safety Operation Plan by Preventing Overcharge During Relaxation Time" [45].…”

“…Consequently, the maximum SOC difference increased from 2.84% to 5.06%. The SOC difference in series-connected batteries leads to voltage redistribution in the CV region due to their different DCIRs [7]. Table 4 shows the simulation results for a serially connected battery with an allowable capacity deviation of ±3%.…”

Battery management system enhancement for lithium-ions battery cells using switched shunt resistor approach based on finite state machine control algorithm

“…As a result of the proposed solution, a wider range of battery-capacity deviations will be permitted. With Simulink simulations, we identified problems, suggested improvement measures, and identified improvement measures to verify the proposed method (Yun and Kee, 2023).…”