Research On Energy Equalization Technique Of Pure Electric Vehicle

Lithium-ion batteries, especially the ones used for pure electrical vehicles, although being at the same level at first, gradually differentiate under the effect of complex electrical charge and discharge conditions, combined with the single in the group actually being at different temperature, which results in sharp decline in battery pack performance. The application of equalization technique is considered as the most effective way to relieve the problem. However, due to inherent constitution, external characteristics parameters and coupling effect, there has always been great disagreement about balancing target and balanced degree criterion. Defective topology and obscure strategy directly hinder the practical application of equalization technique. Therefore, it’s urgent to take a deep study on equalization technique.Firstly, the thesis studies the performance parameters, their variation and analyzes the cause of inconsistency, the impact of inconsistency and the solution in order to determine the equalization target variable. Then comparatively explores SOC estimation methods and decides to estimate remaining charge/required charge by PNGV model, EKF filtering algorithm and revised actual capacity.Secondly, the thesis comparatively researches the advantages and disadvantages of existing topology and proposes novel hierarchical structure based on single inductor and single transformer topology. In the development of balancing strategy, takes battery constitution into account and categories balancing operation into overbalanced, just balanced and underbalanced to reduce energy transfer loss.Finally, the thesis validates the equalization scheme through independently designed experimental platform. By comparison with no balancing, novel hierarchical structure plus closed circuit voltage balancing, the proposed equalization scheme proves efficient to enhance charge and discharge of battery pack.