| Lithium ion batteries usually are used in series or parallel connection due to capacity constraints,and parameters of lithium batteries will be inconsistent with the impact of internal uncontrollable chemical reaction of batteries.These will make the single cell overcharged or overdischarged in the charge and discharge cycles and affect the performance and life of the lithium battery pack.So ensuring the lithium battery monomer can be effectively balanced has become a research focus of new energy vehicles at present.The equalization charging scheme using quasi resonant for lithium battery is improved in this paper based on the extensive research.In the meanwhile,the data collected by the battery management system is transmitted by using the RF wireless technology.The main research work of this paper is as follows:(1)The characteristics of lithium batteries and reasons of inconsistency of battery pack have been analyzed and the scheme of equalizing charge at the beginning of charge and discharge cycle is proposed.A kind of improved active equalization charging scheme for lithium battery based on resonant circuit is proposed through comprehensive comparative analysis of the advantages and disadvantages of various passive and active equalization schemes.(2)The principle of active equalization charging circuit,the zero current quasi resonant circuit for reducing switching loss of MOSFET and the application of auxiliary balancing module are analyzed.The equalization charging scheme has been simulated by using SimPowerSystem toolbox in the software of Matlab/Simulink.(3)The circuits have been designed according to the pin function and characteristics of the main control chips like AD7280A,MC9S12XDP512,etc,including the circuit getting voltage,temperature and current of batteries,power supply circuit,SPI and SCI communication circuit,active charge equalization circuit and the minimum working circuit for the chips.And the hardware circuit of BMS is built by using the RF wireless transmission module of NRF24L01.(4)The program was compiled based on the hardware circuit,including the main program,the program getting working parameters of batteries,the wireless transmission program,and so on.The program of host computer interface on PC was compiled by using the software of Lab VIEW.(5)The charge and discharge experiments were conducted for the 6 string lithium battery,and the preliminary active equalization charging experiment was conducted for the 2 string lithium battery.The improved active equalization charging scheme can effectively keep the terminal voltage of the lithium batteries consistent in charge.And these will provide certain reference for the research on the equalization of lithium batteries. |
