Research On Charge Equalization System Of Series Connect Lithium-ion Battery

With the rapid development of the science and technology in today’s society, new power, energy saving and environmental protection have become the new target of the electric car research, it is a new and dynamic development direction as well. Because of the advantages that many other battery can’t compare with, lithium battery will be widely used as an important part of power of automobile. The voltage of single lithium battery is low and can’t meet the actual demand of the electric vehicle. Generally, series battery packs are used as the way to reach the supply voltage. Because of the battery monomer attribute characteristics between each cell, such as:the difference of the initial capacity, voltage and coulomb efficiency, Through a period of use, the differences of each cell present to be bigger and bigger due to the initial capacity, voltage and coulomb efficiency can not be exactly consistent, so that the battery can’t work very well. It is visible that the balance relationship between the each battery critical for the steady and efficient use of the car. The study of equilibrium charging system of battery pack has practical significance to promote the evolving of the electric car.In this paper, the equalization technique system of Li-ion battery pack is the core of the research. Through the study of working principle, charging characteristics, battery modelling and research of charging method of the lithium battery, combined with the existing problems of the equilibrium solution in the process of use, comprehensively arrangement, a new steady and efficient battery equalization system is put forward, the inconsistency has been improved.First of all, bi-directional equalization charging system is designed. Energy equilibrium between adjacent two batteries can be realized use this system. Equilibrium charging system is composed of detection unit, control unit and balance unit. Through the detection of voltage and charging current and other characteristic parameters of battery using test unit, control unit get the detected results, these parameters are analyzed. By controlling the corresponding MOSFET tube cut-off and conduction, the control of the whole battery equalization is completed.Secondly, considering the fuzzy-PI control to the applicability of the equalizing charge system, in order to the further optimize of the equalization system, the fuzzy PI control theory is applied to the electric car lithium-ion battery equalization charging system, the corresponding equalization charging control algorithm is designed. The complex system can be organized control use the algorithm, the control effect is good.Finally, the batteries series equilibrium charging fuzzy-PI control system based on Matlab/Simulink platform has been designed. Then the simulation experiment is carried out. According to the experimental result, we conclusion that the battery equalization system and equilibrium charging fuzzy-PI control arithmetic has good effect on the lithium battery pack, reduces the difference between the battery cells, prolong the service life of the battery, prevents monomer battery from over-charge and over-discharge,verifies the effectiveness of the equilibrium system and equilibrium control algorithm, achieves the purpose of the balance of lithium-ion battery pack charging.