Abstract
As a critical subsystem in electric vehicles and smart grids, a battery energy storage system plays an essential role in enhancement of reliable operation and system performance. In such applications, a battery energy storage system is required to provide high energy utilization efficiency, as well as reliability. However, capacity inconsistency of batteries affects energy utilization efficiency dramatically; and the situation becomes more severe after hundreds of cycles because battery capacities change randomly due to non-uniform aging. Capacity mismatch can be solved by decomposing a cluster of batteries in series into several low voltage battery packs. This paper introduces a new analysis method to optimize energy utilization efficiency by finding the best number of batteries in a pack, based on capacity distribution, order statistics, central limit theorem, and converter efficiency. Considering both battery energy utilization and power electronics efficiency, it establishes that there is a maximum energy utilization efficiency under a given capacity distribution among a certain number of batteries, which provides a basic analysis for system-level optimization of a battery system throughout its life cycle. Quantitative analysis results based on aging data are illustrated, and a prototype of flexible energy storage systems is built to verify this analysis.
Highlights
With fast-growing distributed generation (DG) in recent years, smart grids have evolved into a comprehensive networked system composed of renewable resources, energy storage systems, and loads
This study provided a theoretical support to calculate the energy utilization efficiency of Battery energy storage systems (BESS)
It is known that among the large number of battery samples, if more batteries are connected in series, the average voltage of the batteries is closer to average level of samples
Summary
With fast-growing distributed generation (DG) in recent years, smart grids have evolved into a comprehensive networked system composed of renewable resources, energy storage systems, and loads. A certain number of modules can be conventional cascaded orgroup parallel-connected to a DC bus or AC bus In this case, high consistency is only required inside each low-voltage battery pack with N/n batteries (assume that all groups have the same size).Power. There was only one case studied in the paper, and the relationship between energy utilization efficiency and the number of batteries in one pack was still not clear. Based on the statistical characteristics of batteries’ data, calculation of energy utilization efficiency after a certain number of batteries are divided into several groups is feasible in this paper. UO (terminal voltage) reaches the cut-off voltage ahead of UOCV because of UR and UP , which means that the battery will not be fully charged/discharged
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