Abstract
The power from lithium-ion batteries can be retired from electric vehicles (EVs) and can be used for energy storage applications when the residual capacity is up to 70% of their initial capacity. The retired batteries have characteristics of serious inconsistency. In order to solve this problem, a layered bidirectional active equalization topology is proposed in this paper. Specifically, a bridge-type equalization topology based on an inductor is adopted in the bottom layer, and the distributed equalization topological structure based on the bidirectional BUCK-BOOST circuit is adopted in the top layer. State of charge (SOC) is used as the equalization target variable, and the bottom layer equalization algorithm based on a “partition” idea and route optimization is proposed. The static equalization experiments and charge equalization experiments are performed by the 12 retired batteries selected from an electric sanitation vehicle. The results show that the proposed equalization method can reduce the SOC difference between retired batteries and can effectively improve the inconsistency of the retired battery pack with a faster equalization speed.
Highlights
The number of electric vehicles (EVs) has grown rapidly due to increasing anxieties of environment deterioration and shortages of fossil fuels in recent years
Bottom layer equalization time was about 2625 s, equalization time of the whole retired battery pack was about 4925 s; as shown in Table 4, at the end of the equalization, the State of charge (SOC) range was decreased to 1.41%, the average of SOCs was 86.91%, maximum deviation from average was decreased to 0.87%, and standard deviation was decreased to 0.42%, r was decreased to 0.467%
This paper proposes a layered bidirectional active equalization method based on the SOC of batteries
Summary
The number of electric vehicles (EVs) has grown rapidly due to increasing anxieties of environment deterioration and shortages of fossil fuels in recent years. Dual-inductor based charge equalizer energy is proposed for transfer energy from high-voltage cells to the battery module directly in [24]. A multi-switched inductor equalization circuit is designed in [25], and an inductor based equalization circuit is proposed in [26] for constant-voltage/current charging and discharging, their topologies are simple and easy to control, but could only transfer energy between adjacent batteries. Due to the large number and serious inconsistency of retired batteries, in this paper, a novel layered bidirectional active equalization topology based on inductor for retired batteries for energy storage is proposed. The numerical results have shown that the proposed method is suitable for the equalization of retired lithium-ion batteries for energy storage applications
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