Research On State Estimation And Balance Management Of Power Lithium Battery

Power lithium batteries are being applied in blade electric vehicle industry as main storing devices of electric powers, the real-time status of which are required to be comprehended to determine potential endurance of vehicles range and lifetime of batteries. Due to the limitations of present battery technology, the safe and effective performance of over-all properties for power lithium battery are usually decided based on power lithium battery state estimation and the balanced management level. Unfortunately, parameters such as inner resistance and etc. for lithium batteries that are nonlinear dynamic system actually, may not be kept unchanged because of factors such as environmental temperature, aging and so on in the process of charging and discharging, which may make it quite difficult to estimate State of Charge (SOC) of lithium batteries. On the other hand, power lithium-ion batteries are applied in the form of a pack with individual differences between each other, which may result in lower efficiency and cycle life expectance compared to the case of single one.In order to improve service efficiency and numbers of duty-cycle operation for power lithium batteries, it becomes necessary to manage a power lithium battery pack with equilibrium. Consequently, the main research contents are included as follow:First of all, the advantages and disadvantages of the common power lithium battery models have been analyzed in order to establish a more accurate power lithium battery model. Based on the analysis, an equivalent circuit model has been chosen, and optimization and improvement has been done correspondingly. For feasibility and accuracy verification and estimation of the power lithium battery model, experiments have been carried out to a power lithium battery of certain type since it is very important to investigate characteristics power lithium batteries for estimating the power lithium battery's SOC and the equalization of battery research.Secondly, advantages and disadvantages of SOC have been analyzed. Based on the improved RC equivalent circuit model, SOC and internal resistance of a power lithium battery have been estimated by Dual extended Kalman Filter (DEKF). And the other parameters for the RC equivalent circuit model have been updated with just estimated internal resistance to promote the precision of SOC estimation.Finally, based on the analysis of reasons for inconsistencies of different dynamic lithium batteries, by choosing an equilibrium circuit formed with switched capacitors mainly as the equilibrium circuit topological structure, taking open circuit voltage and operating voltage as equilibrium parameters, and referring range to evaluation index of equilibrium, four equilibrium management strategies have been formulated called "equal equilibrium", "average equilibrium", "top equilibrium" and "bottom equilibrium" under possible operation status respectively. Meanwhile, efficiency of the equilibrium management strategies has been verified with MATLAB simulation.