State-of-Charge Inconsistency Estimation And Equalization For Large-scale Li-ion Battery Pack

Environmental pollution has become one of the major problems that restrict healthy development of economy and society,therefore it is important to create a greener energy structure.Li-ion battery is the most widely used renewable energy storage devices which plays an important role in energy structure.In order to maximize capacity utilization and guarantee safe operation of Li-ion battery pack,state-of-charge(SOC)inconsistency estimation is essential.And estimating cell electrochemical internal variables is also the requirement of next generation battery management system(BMS).However,it is challenging for the BMS in electric vehicles due to dynamic current conditions and limited computational resources.We propose a novel approach to estimate SOC inconsistency for Li-ion battery pack with reference-plus-difference model where the reference model represents the overall performance of the battery pack.An electrochemical model is used as the reference model for its high-fidelity,low parameter sensitivity,and the capability of estimating cell electrochemical internal variables.Then SOC difference of each battery is achieved by bias correction technique using readily available measurements.The proposed approach is verified by experiments and simulations which show a satisfactory balance between estimation accuracy and computational burden.The state-of-charge inconsistency needs to be balanced in order to maximize capacity utilization and guarantee safe operation of Li-ion battery pack.We study present battery balance methods and choose the switched capacitor circuit for its low cost and small size.Based on the basic structure,we proposed a new switched capacitor circuit.Then the proposed circuit is analyzed and verified by experimental tests which show an improved performance.