Equalization System Development And Balancing Strategy Research For Lithium-ion Power Battery Pack Used In Electric Vehicle

As air quality issue in city has been increasingly highlighted and the oil resources have been increasingly scarcity, Electric Vehicle has received more and more people’s attention. Because of its excellent performance, the Lithium-ion battery cell is used in electric vehicle as energy carrier. However, while packed, capacity utilization of the Lithium-ion Power Battery Pack and circuit life have been heavily discounted compared to single cell due to inconsistency of cells. At present, as one of the effective methods to solve the inconsistency problem, battery balancing management has become a research focus. This thesis has targeted to the development of balancing system and equalization strategy. The specific contents are listed as below:1.Firstly, The operation principle of the battery is introduced in this thesis, and then the performance difference of battery under different circulating charge and discharge test has been studied; A comparison and analysis of several common used SOC estimations has also been shown in the thesis; Besides, the reason for capacity fading has been analyzed and the necessity of capacity correction has been proposed.2.The thesis analyzes the influencing factor, form of expression and impact of battery inconsistency, then the control methods are proposed.3.The design of balancing system scheme is divided into two part:design of balancing topology circuit and equalization strategy. First, three common balancing topology are studied and compared, and then based on buck-boost, flyback converter and single-core transformer, a new balancing circuit and its parameter are designed; Secondly, remaining capacity is chose as Balanced variable and open voltage method is used to estimate the value of cell SOC, a method to modify the capacity of cell is proposed. Finally, equalization strategy used to balance energy among the cell modules as well as cells in a single module are proposed.4.Finally, the proposed balancing module is integrated into the BMS. Then from hardware side and software side, the overall BMS is designed and the test platform is set up, based on which, the balancing test is executed to verify the balancing scheme.