Inconsistency and Health Condition Monitoring of Lithium-Ion Battery System for Vehicles

The consistency and health condition are important to the safe, reliable and efficient operation of the battery system in electric vehicles. The main cause of the cells' inconsistent characteristic in a battery pack is analyzed. After the evolution of the inconsistency is established, its influence on the battery health condition is also analyzed. The library of equivalent circuit models and the general parameter optimization method of lithium-ion battery are established. In order to systematically evaluate the accuracy and adaptability of these models, the hybrid pulse power characteristic (HPPC) experiment is carried out to identify the parameters of these models and estimate the battery status. Compared with the original data, all the root mean square error (RMSE) of these models are lower than 16 mV. The battery display terminal is developed to carry out the application and validation of the algorithm. The feasibility of the evaluation system is verified by experimenting with 12 selected single cells in series. Results show that all the 12 batteries have a good consistency with the standard deviation of 0.007 A•h and the capacity decline rate is 12% after 800 charge and discharge cycles.