Research On Lithium Battery Equalization Technology Based On Double-Layer Structure

Lithium-ion battery is a key technology in photovoltaic power generation,electric vehicles and other new energy fields.In practical applications,battery cells are usually combined in series and parallel to form battery packs.Due to differences in production and operating conditions,there is inconsistency among battery packs,which will reduce the effective capacity and service life of battery packs.Even lead to battery fire,explosion and other safety problems.The battery equalization is an important part of Battery Management System(BMS).It is necessary to study how to improve the equalization effect and reduce the inconsistency between battery cells in a shorter time.Aiming at the defect of DC2C(Direct Cell to Cell)structure that the equalization speed is limited due to fewer equalization paths,a double-layer active equalization circuit topology is proposed by combining improved resonant circuit and Buck-Boost circuit with multiple switched inductor.The equalization circuit topology is divided into top layer and bottom layer,and the equalization process of the two layers does not affect each other.The increase of equalization paths can increase the equalization speed effectively.The top layer adopts an improved resonant equalization circuit,which introduces a third operating mode through connecting switch at both ends of LC in parallel.This operating mode can release the charge in the capacitor and restore the capacitor to the initial state of the cycle.The balanced current is no longer limited by the voltage difference of batteries.The equalization rapidness is greatly improved compared with the traditional resonant circuit,and soft switching can be realized,reducing circuit switching loss;the multiple switched inductor Buck-Boost equalization circuit is used in the bottom layer.Compared with the traditional Buck-Boost equalization circuit,it has a simple structure,fewer components and is suitable for balancing a small number of batteries.Firstly,this paper introduces the working principle of two kinds of equalization circuit,carries on modeling analysis respectively,gives the expression of equalization current and equalization efficiency,the factors affecting equalization performance are analyzed and the parameter design suggestions are given.Then the balance control strategy based on the double-layer topology with battery voltage as the balance variable is designed.The theoretical analysis of the circuit and the effectiveness of the topology are verified by MATLAB/Simulink software.Finally,a lithium battery equalization experiment platform was built.The traditional resonant equalization circuit,the improved resonant equalization circuit,the multiple switched inductor Buck-Boost equalization circuit and double-layer equalization circuit were carried out respectively.The experimental results show that the improved resonant equalization circuit can effectively improve the defects of the traditional resonant equalization circuit and the double-layer equalization circuit can quickly and efficiently complete the battery equalization.The feasibility of the proposed equilibrium scheme is verified.