Research On Active Equalizer For Lithium Battery Pack Of Electric Vehicle Based On Layered Series

In recent years,the implementation of the "double carbon" policy has promoted China’s new energy technology and industry has made great progress.Especially the application of lithium battery has become the core power source of new energy electric vehicles,which has received wide attention and attention from all walks of life around the world.In order to meet the voltage and power requirements of new energy electric vehicles,it is often necessary to use multiple lithium battery cells in series and parallel.However,due to the inconsistency between each battery cell,some of the batteries may be overcharged or over discharged after multiple charges and discharges,which will greatly reduce the reliability of the entire battery system and shorten its service life.If effective measures are not taken,it may even cause serious safety hazards.Therefore,it is important to develop a safe,efficient and reliable battery equalization control system to improve the inconsistency between battery cells.Based on the analysis of the existing active equalization circuit,this paper takes improving the efficiency and equalization speed of inter-lithium battery equalization as the starting point of research,integrates two different equalization topologies,and designs an efficient hierarchical equalization control system.The equalization system divides the equalization methods into two types: intra-module equalization and inter-module equalization.Two-way Cuk equalization circuit structure is adopted in the module,and the same core multi-winding flyback converter equalization structure is adopted between modules.This article first analyzes the working principle of the equalization circuit within the module,derives the formula for the circuit’s working characteristics,and analyzes the voltage and current stress of its corresponding devices.In addition,based on the characteristics of the equalization circuit,a dual closed-loop control strategy was adopted,and a detailed introduction was given on how to model the circuit using the state space averaging method and design inner and outer loop controllers.And through simulation verification,it is found that this control strategy can significantly shorten the equilibrium time and have good stability compared to traditional control strategies.Then,the working principle and mode of the inter-module equalization circuit are analyzed in detail.The influence of non-ideal factors in the circuit on the inter-module equalization circuit is studied,and the equalization principle and operating characteristics of the inter-module equalization circuit considering leakage inductance are analyzed.In addition,according to the inter-module equalization circuit and the overall working characteristics of the system,the inter-module equalization strategy and the system coordination control strategy are determined.After simulation verification,it was found that the simulation waveform is completely consistent with the theoretical analysis,and the proposed topology and control strategy can quickly achieve balance between batteries.In terms of balance time,it requires less balance time than traditional single-layer balance.Finally,based on the analysis of the above equalization principle,the hardware and software of the equalization system are designed and an experimental prototype of a fourcell battery based on STM32 control is built.The working principle of each equalization circuit and the equalization control strategy are verified accordingly according to the experimental prototype built.