Study on Battery Fast Charge and Discharge Model and its Parameters

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1 Send Order for Reprint to The Open Electrical & Electronic Engineering Journal, 204, 8, Open Acce Study on Battery Fat Charge and Dicharge Model and it Parameter Lun-qiong Chen,*, Lu-lu Du 2 and Bei Li School of Electronic Information and Electrical Engineering, Changzhou Intitute of Technology, Changzhou, 23002, China 2 School of Electronic Information, Wuwei Occupational College, Wuwei, , China Abtract: In order to tudy the battery performance, putting forward a kind of two order RC equivalent circuit model, meauring tatic and tranient data by HPPC tet, fitting the relationhip between open circuit voltage and tate of charge (SOC), analyzing ytem identification of the dynamic parameter with MATLAB tool. Finally, by comparing the imulation data with the tet data, the model i correct and feaible. Keyword: Battery, dynamic model, open circuit voltage, tate of charge (SOC), ytem identification.. INTRODUCTION Becaue of environmental pollution need, electric vehicle aroued more attention for energy aving and environmental protection. With the popularization of electric vehicle, the battery charging and dicharging technology i epecially important. The battery model i the key factor of charge and dicharge of the battery. After defining model parameter through ytem identification, it can imulater charge-dicharge and reflect the real performance tatu of battery, o a to tudy the battery capacity, circulation ervice life, elf dicharge rate and (SOC) etc [, 2]. 2. SELECTING MODEL Modeling of the battery ytem mainly include electrochemical model, artificial intelligence model and equivalent circuit model [3]. Etablihment of model required high accuracy, little calculation work and achieving eaily parameter. Therefore, an intuitive and accurate equivalent mathematical model wa preented on the bai of the two order RC equivalent circuit model [4], a hown in Fig. (). In Fig. (), left ide of the circuit wa on behalf of battery capacity, tate of charge (SOC) and the operation time of battery; right ide of it wa tranient tate. The controlled voltage ource wa characterized with the nonlinear relationhip between the SOC and the open circuit voltage. wa the open circuit voltage. wa the ohmic reitance, tanding for lo energy for long time, and could conider to infinity becaue of little impact by elf dicharge. wa capacity of the battery. wa charge or dicharge current. Baed on circuit diagram, ordinary differential equation of the mathematical model were built: = + = In equation, tate variable of thi mathematical model were repreenting the open circuit voltage of the battery, U t repreenting voltage of and U t reprenting voltage of, the battery charge or dicharge current a input, the voltage a output. 3. THE EXPERIMENT The experiment were proceed on fixed temperature (25 ±2 C) for everal day. Selecting three lead-acid batterie 6-MQ-7D (2V7AH), BTS-M 300A/2V and BTS-M30 A/48V teting device. The Hybrid Pule in Power Characterization (HPPC) of "Freedom CAD battery tet manual" wa ued to complete charge and dicharge tet [5]. The HPPC can tet dynamic power by pule charge and dicharge tet ytem. The dicharge tet ytem adopted in the experiment: () /4 204 Bentham Open

2 368 The Open Electrical & Electronic Engineering Journal, 204, Volume 8 Chen et al. Fig. (). Equivalent mathematical model of the battery. Fig. (2). The ingle cycle pule dicharge. Firt, charging to full SOC uing three tage contant current-contant voltage method and then holding for one hour at 25 C temperature. Second, dicharging 0% (0.7Ah) of battery capacity by C(7A) and then holding for one hour, SOC wa 0.9. Third, dicharging for 0 econd by 2C(4A) and then holding for 40 econd, charging for 0 econd by.5c(0.5a) and then holding for 0 econd. Thi proce i hown in Fig. (2). Fourth, repeating the tep econd and third, each proce releaed 0% battery capacity and repectively SOC wa 0.8, 0.7, to the end of the tet. The HPPC charging proce wa imilar to the dicharging proce. Beginning Charging proce after dicharging to the cut-off voltage and holding four one hour, then replace dicharging to charging in the econd. The following tudy would revolve mainly around the dicharge proce. 4. SYSTEM PARAMETERS IDENTIFICATION Some unknown parameter of dynamic mathematical model in Fig. () were not certain becaue of SOC, the temperature of the environment and the cycle life of the battery. But conidering the influence of SOC in a table environment temperature and for everal day. 4.. The Relationhip Between the Open Circuit Voltage and SOC When there i no current through the battery, the potential difference between two pole i the open circuit voltage (OCV). After the HPPC tet, the battery wa in holding tate for one hour and the current wa zero, then the polarization voltage would be gradually eliminated and the terminal voltage continued to rie. Fig. (3) howed the voltage curve after holding for one hour.

3 Study on Battery Fat Charge and Dicharge Model The Open Electrical & Electronic Engineering Journal, 204, Volume Fig. (3). The voltage curve after holding for one hour. Fig. (4). Voltage repone curve of HPPC. In Fig. (3), after dicharging, the terminal voltage ried rapidly to 80% of table voltage in a hort time, then the rate of riing decreaed gradually and it kept table at the end. So electing the holding voltage for one hour a open circuit voltage. The meaured data howed the curve between the open circuit voltage and SOC wa relatively fixed. Averaging the meaured data of three battery and uing the leat quare fitting to derive equation 2: = + + (2) 4.2. Identification of the Dynamic Parameter In Fig. (), reitance and capacitance were related to SOC. So, earching the repone voltage curve according to SOC, then fitting the curve by fitting toolbox in the MATLAB oftware and combining with the model equation to get the unknown parameter value in the model. A hown in Fig. (4), voltage repone curve wa under HPPC cycle pule dicharge charge when SOC wa 0.8. There were holding tate during 0 to 0 econd, 20 to 60 econd and 70 to 80 econd. There were pule current dicharge during 0 to 20 econd and pule current charging. A an example to illutrate the identification proce of all kind of parameter [6]. The circuit in Fig. () howed capacitor terminal voltage wouldn t change at tart moment during changing or dicharging and current only flowed through reitance R. So in Fig. (4), the voltage wa caued by reitance

4 370 The Open Electrical & Electronic Engineering Journal, 204, Volume 8 Chen et al. K -/(RtCt) /Ct Add Integrator 2 icell -R Ucell /Ccap Integrator -/Ctl Add2 Integrator Add K -/(RtlCtl ) Fig. (5). Simulation circuit of the battery model. R when pule current began dicharging at ten econd. Similarly the voltage wa alo caued by reitance R when pule current dicharge completed. Due to the impact of dicharge proce, the value of and were not ame. (3) In Fig. (4), there wa holding tage after pule dicharging for 20 to 60 econd and the current in the circuit i zero. and circuit were zero input. We had = (4) In equation 4, and were voltage when dicharging intantly. =, =. The leat Square Fit wa applied to calibrate and uing voltage curve in 20 to 60 econd by MATLAB toolbox. In Fig. (4), becaue of holding one hour before, and circuit were zero tate repone during pule current dicharge in 0 to 20 econd. At thi time, = (5) The leat Square Fit wa applied to calibrate and uing pule current dicharge curve by equation 5 and MATLAB toolbox. Then and could be obtained from = and =. Parameter identification of the battery model reulted a hown in Table, the parameter,,, and depended upon SOC. 5. MODEL VERIFING In order to verify the parameter identification, building the imulation model in Matlab/Simulink, A hown in Fig. (5). According to the Simulink model in Fig. (5), uing contant current dicharge to imulate and compare with experimental data. The curve of tet dicharge wa the ame a imulation curve under the ame dicharge rate of battery. Thi howed that mathematical model could be fitted well to the the actual operation of the battery and the identification method wa feaible. CONCLUSION Putting forward more intuitive and accurate circuit model of battery and completing ytem parameter identification baed on the mathematical model now. Through MATLAB

5 Study on Battery Fat Charge and Dicharge Model The Open Electrical & Electronic Engineering Journal, 204, Volume 8 37 Table. The reult of model parameter identification of dicharge. SOC imulation, comparing the imulation data and the experimental data and verifying the correctne of the model to be applied to etimate SOC. CONFLICT OF INTEREST The author confirm that thi article content ha no conflict of interet. ACKNOWLEDGEMENTS Thi work wa financially upported by Science and technology upport program of Changzhou (Program No. CE , ) and the program of Changzhou Intitute of Technology (Program No.YN08, and YN35, ). REFERENCES [] L. Zhao, The Battery Dictionary, Beijing: Chemical Indutry Pre, 202, pp [2] C. Q. Gui, Power Battery, Beijing: China Machine Pre, 2009, pp [3] Z. L. Yang, G. Q. Zhang, Z. L. Wang, The modeling method of high capacity lead-acid torage battery, Marine Elect. Electron., vol. 32, pp , Jun [4] Y. Q. Zhang, K. Guo, H. Y. Liu, Reearch on equivalent model and it parameter identification of lead-acid batterie, Chin J. Power Source, vol. 50, pp , Mar [5] M. Chen, G.A. Rincon-Mora, Accurate electrical battery model capable of predicting runtime and I-V performance, IEEE Tran. Energy Conver, vol. 2, pp , Feb [6] G. L. Wu, Z. Y. Zhou, D. R. Yu, Unteady open circuit voltage method for tate of charge etimation of electric vehicle batterie, Elect. Mach. Cont., vol. 7, pp. 0-5, Apr Received: October 6, 204 Revied: December 23, 204 Accepted: December 3, 204 Chen et al.; Licenee Bentham Open. Thi i an open acce article licened under the term of the Creative Common Attribution Non-Commercial Licene ( which permit unretricted, non-commercial ue, ditribution and reproduction in any medium, provided the work i properly cited.