Research And Development Of Battery Management System For Prolonging The Life-cycle

Our lives got improved and social development got promoted with the development ofautomotive. With the trend of sustainable development, auto brings three major challengesfor sustainable transport: energy, environmental and safety problem. Gradually people putthe attention on new energy vehicles, especially on Hybrid Electric Vehicles (HEV) andElectric Vehicles (EV), whose research and development technology are matured and havebeen put into market operations. With the in-depth research on HEV and EV, the powerbattery has also become a hot research topic. At present, the power batteries used on newenergy vehicles mainly includes lead-acid batteries, nickel cadmium, nickel metal hydridebatteries and lithium-ion battery. These power batteries have achieved remarkableachievements in the monomer manufacturing process, their energy density and powerdensity get increased as well as their life cycle. Nevertheless, there is a big gap between ourdesired goals and its performance no matter what power battery it is. For that reason, peoplestart to research how to manage and use battery reasonably, hoping for making sometechnological breakthrough in battery management which can compensate for the lack ofbattery technology. The battery management system has become a sub-direction of thebattery technology. The battery cycle life is always the bottleneck in the development of newenergy vehicles. In view of this circumstance, this paper studied the management system oflithium-ion battery pack deeply for prolonging its life cycle. The main contents of this paperare as following.1. Consult the progress of domestic and foreign in the cycle life of the battery pack,and get the main relevant influence factors of the cycle life of the battery pack: the chargeand discharge rate, the depth of discharge and the homogeneity of the single battery. Chargeand discharge rate exceeds the bearing capacity of the battery pack, the unreasonable controlabout the depth of discharge, are two kinds of battery abuse. Battery monomerinconsistencies would result in the short-board effects of the battery pack. They all affect the life cycle of the battery pack seriously.2. Take iron phosphate lithium battery as the research object, build lithium-ion batterynonlinear equivalent circuit model according to battery features, and make use of circuitschematic knowledge to analyze the dynamic response of the model under the step input.Then design parameters identification experiment on the basis of the results of this study,and use mathematical Curve Fitting Tool of Matlab to identify the model parameters. Build abattery model on the simulation platform Matlab/Simulink, and then verify model selectionreasonable and identification method valid by comparison of experimental data andsimulation data.3. Give a detailed functional analysis on Battery management system, based on thedesign concept of the distributed topology structure, and divide the batterymanagement system into several sub-control units and a main control unit. Sub-controlunit is responsible for the voltage and temperature collecting of battery monomer, balancecontrolling, the total voltage collecting, the total current collecting and leakage detecting, inthe mean time the main control unit is more concerned about the overall states of the batterypack, such as the estimate of SOC, the estimate of charge and discharge current accordingto the SOC, the power supply management of sub-control unit, high-voltage relay control,and the information exchange with other controllers of the vehicle. Then select theappropriate type of hardware based on the functional requirements of the control unit andcomplete the hardware circuit design.4. In order to extend the cycle life of the battery, according to the influence factorsanalysis for the battery pack, the paper design the software part of the BMS, includingmonomer balancing control, real-time estimation for SOC and the available current duringthe charge and discharge. Come up with the most optimization principle in the aspect ofmonomer balancing, and add the standard deviation theory into the balance controllingalgorithm, so we can extend the battery cycle life by improving the monomer consistence ofbattery pack. By estimating the SOC and the available current of charge and discharge, wecould avoid the abuse of the battery in order to extend its cycle life. 5. According to the bench test which is used to verify the BMS designed in the paper,we can prove that the design can extend the cycle life of the battery pack effectively by theevaluations of capacity attenuation and ohm resistance increasing.