Lithium ion battery is the most widely used and reliable power source for electric vehicles. With the development of electric vehicles, the safety, energy density, life and reliability of lithium ion batteries have been continuously improved. However, in the field of vehicle power battery technology, battery monomers are combined in series and parallel to provide enough energy, but one of the major problems faced by group batteries is the consistency between battery monomers. Taking the capacity increment curve (IC curve) of lithium iron phosphate battery as the analysis tool, it is found that the characteristic peak of IC curve of different monomers in battery pack can reflect the relationship of monomer capacity. On this basis, the mathematical model is established, and the IC curve II peak characteristic point of a single cell are used as the reference to characterize the capacity of the single cell one by one. The results show that the method can be used in the normal charging process of the battery pack, and the capacity of the single cell in the battery pack can be characterized in real time during the whole life of the battery pack. It has certain research value for the ladder utilization and accurate management of battery pack.
At present, most of the BMS in the market set a constant fault threshold, but with the increase of the number of power battery recycling, the external characteristics of the battery will also change. A constant fault diagnosis threshold may also occur after battery aging diagnosis is not timely. Battery cell voltage is the direct embodiment of the external characteristics of battery cell, so the fault diagnosis of battery cell voltage is the most important. Too high or too low cell voltage is the most obvious fault. Normally, this should not happen. Of course, due to the gradual aging of the battery pack, the inconsistency between the monomers and the charged state of each cell, the inconsistency of the voltage of each cell can not be avoided. However, the voltage difference caused by cell manufacture or inconsistency is limited in the case of aging degree.Based on the battery discharge data, the purpose of this study is to propose a method to identify the gradual fault signal in advance and reduce the problems caused by the sudden failure of the battery by detecting and diagnosing the change trend of the extreme value difference of the historical operation data.
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