储能系统初始参数和运行环境的差异性，会导致电池单体荷电状态(state of charge，SOC)的不一致性，降低储能系统能量利用率。为解决上述问题，设计了基于双层极值法的锂离子电池均衡实验。采用耦合电感与Flyback变换器搭建均衡系统双层架构，建立电池组端电压、均衡电流及占空比间的关联特性;以储能电池端电压作为均衡目标，提出基于双层极值法的锂离子电池快速均衡方法;搭建电池均衡实验教学平台，设计充放电及静置均衡实验，通过仿真分析和实验数据验证所提方法的有效性。该教学实验将理论知识、实验操作及数据分析相结合，有助于提升电气工程专业相关课程实验的质量和效果。
Design of lithium-ion battery equilibrium experiment for energy storage system based on the double-layer extreme value method
[Objective]Differences exist in the initial parameters and operating environments of energy storage batteries when many individual batteries are connected in series and parallel to form a group.The differences in the battery parameters yield inconsistencies in the state of charge(SOC)of individual batteries,which greatly reduces the energy utilization of the energy storage system and results in a rapid decline in the battery life.To address the SOC inconsistencies during battery operation,this study proposes a lithium-ion battery equalization experiment based on the double-layer extreme value method.[Methods]The double-layer equalization experiment contains bottom-and top-layer equalizations.First,the coupled inductor and Flyback converter are used to build a double-layer structure of the equalization system.The PWM signal is employed to control the turn-on and turn-off states of MOS tubes to realize the charging and discharging equalization of the corresponding batteries and establish the correlation characteristics between the terminal voltage of the battery pack,equalization current,and duty cycle.Second,a fast equalization method for lithium-ion batteries is introduced based on the double-layer polar method.An integrated operational amplifier is designed to collect the battery voltage,and the MOS tube is used for voltage collection.The acquisition circuit of the battery voltage and the driving circuit of the MOS tube are designed using an integrated operational amplifier.The polynomial fitting of the SOC of the battery through the OCV-SOC curve is utilized to obtain a more accurate SOC.The charging state of the storage battery is used as the equalization target to set the equalization threshold.Equalization is determined as being turned on or stopped by investigating the relationship between the maximum value of the difference of the SOC within the energy storage system and the equalization threshold.The equalization logic adopts the simultaneous equalization of the bottom and top layers.Equalization is performed between the batteries with the highest and lowest SOCs.This approach significantly shortens the equalization time and improves the equalization speed.Finally,a battery equalization experimental teaching platform is established using four groups of series-connected 18,650 batteries,an equalization board,and an STM32 MCU.The battery equalization experiment teaching platform is constructed,and the charging,discharging,and static equalization experiments are designed.[Results]The results demonstrate that under the same equalization time,the final power of the double-layer extreme value method and the traditional maximum value method remain similar.However,the former achieves up to a 50%increase in the equalization speed compared to the latter.The double-layer extreme value method effectively reduces the battery inconsistency of the energy storage system and improves the battery's service life.The effectiveness of the double-layer extreme value method for the equalization of lithium-ion batteries is verified via simulation and experimental analysis.[Conclusions]This teaching experiment combines theoretical knowledge,experimental operation,and data analysis;thus,the students can gain an in-depth understanding of the relevant theories of power system energy storage.This experimental method provides a basis for experimental teaching in electrical engineering-related courses.
lithium-ion batteriesdouble-layer extreme value methodequalization experimentcharge-discharge balancingstatic equalization
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