Research On Active Equalization System And State Of Charge Estimation Of Lithium-ion Battery

The application of lithium-ion batteries is becoming increasingly widespread with the continuous development of society.In practical applications,it is necessary to use multiple single cells in series to meet different voltage requirements because the voltage of a single cell is low.However,lithium-ion battery packs are inconsistent,so they need to be monitored and managed in real time.Among them,state of charge estimation and battery pack equalization are the most important.This paper studies the SOC estimation of batteries and equalization of lithium-ion battery pack.The main research work is summarized as follows:(1)An improved two-circuit interleaved parallel architecture for battery equalization topology based on inductance is proposed.In response to the problem that the equalization current in two-circuit interleaved parallel architecture for battery equalization topology will decrease during the equalization process,an improvement is made on the TIPAE topology to obtain an improved two-circuit interleaved parallel architecture for battery equalization topology.The improvement measure is to perform multi-position control on each equalization unit to maintain the equalizing current at a large level without increasing the maximum equalization current.Finally,several groups of comparative experiments were carried out on the balance topology before and after the improvement.The experimental results show that the IM-TIPAE topology can effectively improve the equalization speed of the battery pack.(2)Quantitative calculations were conducted on the energy flow during the active equalization process of the battery pack.The active balancing methods are divided into five types based on the energy flow patterns of battery packs during active equalization.They are series-based cell-cell method,module-based cell-cell method,layer-based cell-cell method,series-based cell-pack method,and module-based cell-pack method.Quantitative analysis calculations were conducted on the changes in the SOC of the single battery during one cycle of the five equalization methods.Finally,experimental verification of five equalization topologies is conducted,and the results show that the LCCE equalization topology has the fastest equalization speed.(3)A SOC estimation algorithm based on SH-EKF is proposed.In response to the problem that the unknown statistical characteristics of noise during SOC estimation can affect the accuracy of the EKF algorithm.A SOC estimation algorithm based on SH-EKF was obtained by combining the EKF algorithm with Sage Husa adaptive filtering and Monte Carlo sampling theorem.The proposed new algorithm can predict and correct noise in real-time,thereby reducing the impact of noise interference on SOC estimation.Finally,experimental verification was conducted on SH-EKF algorithm and EKF algorithm,and the experimental results showed that the proposed new algorithm can effectively improve the accuracy of SOC estimation compared to EKF algorithm.(4)A lithium-ion battery active equalization test platform was built,and the equalization experiments were carried out on the No.1 battery,No.2 battery and No.3 battery in battery pack which has 16 lithium-ion batteries in series.The results show that the equalization effect is good and the system can work reliably.This paper provides theoretical support for the rapid balancing of lithium-ion battery packs,and has certain reference significance in solving important engineering issues such as battery inconsistency and slow balancing speed in new energy vehicles.