Improved SOC Estimation And Multi-layer Bi-directional Active Equalization Method In Lithium-ion Power Battery

Energy consumption and pollution are the huge bottleneck to the development of automobile industry, thus the electric vehicles which consuming low power and causing less pollution have become one of the most recognized direction of the development in automotive industry. Due to the reason of large capacity, high energy density, long cycle life, and cost performance, lithium battery has become the mainstream power battery in electric vehicles among numerous batteries. Even so, lithium battery still has the disadvantages of small cell voltage, being very sensitive to temperature, over-voltage, over-current and so on. Mean while, the performance of Lithium-ion activated can easily result in instability and insecurity which cause system control more difficult. Therefore, the technology of power lithium battery management becomes the key point to improve electric vehicles.State of charge (SOC) is the most important parameters to characterize the status of battery. Because of the nonlinearity and instability of dynamic process, the existing SOC estimation methods can’t meet the need of practical application. Therefore, this paper proposes a multi-method fusion algorithm of higher precision and lower complexity. Firstly, a mechanism module is built of which parameters are indentified by recursive lease squares algorithm with a factor of fading memory. Then, through the analysis of advantages and disadvantages of physical and intelligent algorithm, a multi-method fusion SOC estimation method was proposed, which containing Ampere-hour method, Open-circuit-voltage method and Kalman filter method. Finally, this method was verified to have good efficiency through the simulation experiment.Battery equalization is the most effective technology to solve the problem of battery inconsistencies. For this reason, a regional circuit based on capacitor and a multi-layered global circuit based on the fly-back transformer is proposed on the basis of the bi-layer structure in lithium battery. At the same time, to achieve bidirectional self-balancing goals in the process of charging and discharging, a high-precision criterion of SOC was desired and, considering the effect of the process of charge, a factor of SOC distribution was added in the criterion. Finally, effectiveness of the equalization method is verified through a simulation experiment.