Mathematical Model and Experiment of Temperature Effect on Discharge of Lead-Acid Battery for PV Systems in Tropical Area

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1 Energy and Power Engineering, 2013, 5, Published Online January 2013 ( Matheatical Model and Experient of Teperature Effect on Discharge of Lead-Acid Battery for PV Systes in Tropical Area Boonyang Plangklang *, Pornchai Pornharuthai Departent of Electrical Engineering, Faculty of Engineering, Rajaangala University of Technology Thanyaburi, Thanyaburi, Thailand ail: * boonyang.p@en.rutt.ac.th Received Septeber 30, 2012; revised Noveber 4, 2012; accepted Noveber 20, 2012 ABSTRACT This paper presents Matheatical Model and Experient of Teperature effect on Charge and Discharge of Lead-Acid Battery perforance in PV syste power supply. To test teperature effect on battery discharge cycles, a teperature range of tropical area fro degrees Celsius in a siulator is set up for testing. This teperature range is norally practical for battery usage. This allows the battery to deterine the paraeters of the battery quickly and high accurate. A Matheatical Model with MATLAB Progra is written and constructed as block diagra using the equations of battery the paraeters. By running progra, the effects of various paraeters are investigated. The results showed that tie of discharge the battery is longer. Then, the experient is set up by battery VRLA 12 V 20 AH. The results confired the atheatical odel siulations. Keywords: Matheatic Model; Teperature Effect; Lead-Acid Battery 1. Introduction In present situation, energy deand is greatly increasing. Renewable energy is an alternative choice that can be substituted for future energy deand. For PV systes, the battery has iportant role in the process of storing electrical energy. The electrical energy is produced and used in the different tasks depend on the needs of users. Energy used in different places depends on the cliate especially in tropical area. Thus the battery will be needed to aintain the syste stability. The teperature is a ain factor for battery perforance [1-5]. Therefore, it is interesting issue to be studied and analyzed for the property factor of discharge the battery. The atheatical odel is constructed in order to study this issue. It is useful and can investigate to study the paraeters of the battery quickly by siulation then the experient will be ipleented. 2. The Battery Equivalent Circuit The equivalent circuit odel of a lead-acid battery is a voltage source connecting with the internal resistance. (Figure 1) The circuit has a siple structure can be explained because the relationship between the voltage and resistance of the variable parts of the capacitor, state of * Corresponding author. charge (SOC) Teperature, and various eleents of the battery paraeters [6]. Voltage of lead-acid battery per cell produces 2 V. So battery 12 V consists of six cells, so that the next series. Voltage at the terinal will vary according to the conditions of work. And the concentration of the acid will be changed during the charge and discharge [7]. 3. Matheatical Model and the Experient The experient battery by atheatic odel, have the following steps. 1) Study of the battery used in experient, and research data fro the various sources. 2) Designed the circuit test battery and block diagra of atheatical odel using Math Lab progra. 3) Create a atheatic odel progra. 4) Put the equation paraeters in the atheatic odel of battery. 5) Siulate progra for recording paraeters at the teperature fro 25 to 60 degrees Celsius, and recording voltage and current Graph display. 6) Suary conclusions the siulation Block Diagra of Matheatical Model Battery atheatical odel is design by Math Lab. The

2 44 B. PLANGKLANG, P. PORNHARUTHAI C1 C 1 R 1 R 2 R 0 V Rp R p EEp p Main Branch Parasitic Branch Figure 1. Battery equivalent circuit [8]. block diagra of the atheatical odel is used as input current and teperature into the outputs which are voltage, Cell Tep, and the SOC [8,9] as shown in Figure Battery Equation for Matheatical Model Battery equation for atheatic odel will be using to siulate paraeters included Main Branch, Parasitic Branch, Capacity, and Electrolyte Teperature [8-10]. Main Branch 0 (1) 273 KE 1SOC where : E = the open-circuit voltage (EMF) in volts; E 0 = the open-circuit voltage at full charge in volts; K E = a constant in volts/ C; θ = electrolyte teperature in C; SOC = battery state of charge. R R ln DOC 1 10 R 1 = a ain branch resistance in Ohs; R 10 = a constant in Ohs; DOC = battery depth of charge. C R C 1 = a ain branch capacitance in Farads; 1 = a ain branch tie constant in seconds; R 1 = a ain branch resistance in Ohs. (2) (3) R 2 R 20 exp A2 1 1 SOC 1 exp A I I R 2 = a ain branch resistance in Ohs; R 20 = a constant in Ohs; A 21 = a constant; A 22 = a constant; SOC = battery state of charge; I = the ain branch current in Aps; I * = the a noinal battery current in Aps. Parasitic Branch Current I p VPN ps1 VpnGp0 exp Ap 1 V p0 f where : I p = the current loss in the parasitic branch; V pn = the voltage at the parasitic branch; G p0 = a constant in seconds; p = a parasitic branch tie constant in seconds; V p0 = a constant in volts; A p = a constant; θ = electrolyte teperature in C; θ f = electrolyte freezing teperature in C. Charge and Capacity e e_ init t 0 22 (4) (5) Q t Q I dr (6) Q e = the extracted charge in Ap-seconds;

3 B. PLANGKLANG, P. PORNHARUTHAI 45 Ps C1 C1 Tau1 Tau1 C1 Tau1/ Ps I I I Vpn/(Ts+1) Vpn R3 Vpn Vpn I Ps Figure 2. Block diagra of atheatic odel [8]. Q e_init = the initial extracted charge in Ap-seconds; I = the ain branch current in Aps; τ = an integration tie variable; t = the siulation tie in seconds. KC c 0* Kt CI,, I 1Kc 1 I K LUT t K c = a constant; C 0* = the no-load capacity at 0 C in Ap-seconds; K t = a teperature dependent look-up table; θ = electrolyte teperature in C; I = the discharge current in Aps; I * = the a noinal battery current in Aps; δ = a constant. State of Charge and Depth of Charge Q e SOC 1, C 0, (7) Qe DOC 1 (8) C I avg, SOC = battery state of charge; DOC = battery depth of charge; Q e = the battery s charge in Ap-seconds; C = the battery s capacity in Ap-seconds; θ = electrolyte teperature in C; I avg = the ean discharge current in Aps. I avg I 1s 1 I avg = the ean discharge current in Aps; I = the ain branch current in Aps; 1 = a ain branch tie constant in seconds. Electrolyte Teperature (9) a t Ps R t init d (10) C 0 where : θ = the battery s teperature in C; θ a = the abient teperature in C; θ init = the battery s initial teperature in C, assued to be equal to the surrounding abient teperature; P s = the I 2 R power loss of R 0 and R 2 in Watts; R = the theral resistance in C/Watts; C = the theral capacitance in Joules/ C; τ = an integration tie variable; t = the siulation tie in seconds The Experient The experient of lead-acid battery 12 V 20 AH is set up by using teperature control unit and a standard battery discharging syste. The teperature in experient is also controlled in the range of 25 C - 60 C. The dis-

4 46 B. PLANGKLANG, P. PORNHARUTHAI charged current and voltage are recorded by coputer as shown in Figure Results The siulation of atheatical odel uses paraeters of lead-acid battery 12 V, 20 AH. Discharge testing is by final voltage 9.6 V, 20 A, at teperatures ranging fro 25 C - 60 C. The result of the siulation is shown as in Figure 4. Figure 4 shows the results of siulation, battery discharge at 25 C, it takes about 40 inutes to full discharge, at 30 C is about 47 inutes, at 35 C is about 50 Figure 3. The experiental set up. Figure 4. The siulation results of discharged voltage at 25 C - 60 C.

5 B. PLANGKLANG, P. PORNHARUTHAI 47 inutes, at 40 C is about 55 inutes, at 45 C is about 58 inutes, at 50 C is about 62 inutes, at 55 C is about 67 inutes, and at 60 C is 70 inutes to full discharge. It indicates that the discharge tie is longer if the teperature is higher. The experiental results fro the coputer recorded data are shown as in Figure 5. The experiental results indicate the siilarity to the siulation results. The discharge tie was effected by the teperature precisely as on Table 1. Fro Figure 5, at the end of discharge tie, the graph is up again because in the experient even the syste cut off the discharge circuit, the onitoring is still continuously real tie recorded. The experient of entioned lead-acid battery 12 V Figure 5. The experient discharged voltage at 25 C - 60 C. Table 1. Real tie recorded discharge voltage at 25 C - 60 C. Run Tie (Min.) End Voltage (V) and Tep ( C) 25 C 30 C 35 C 40 C 45 C 50 C 55 C 60 C 00: : : : : : : : : : : : : : : : :

6 48 B. PLANGKLANG, P. PORNHARUTHAI Continued 17: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :00: :05: :10: :15: :20: :20: :20:

7 B. PLANGKLANG, P. PORNHARUTHAI AH in Figure 5 is ipleented by discharged current 20 A, at teperatures ranging fro 25 C - 60 C. Battery discharge, at 25 C, it takes about 40 inutes to full discharge. At 30 C is about 45 inutes, at 35 C is about 48 inutes, at 40 C is about 49 inutes, at 45 C is about 50 inutes, at 50 C is about 49 inutes, at 55 C is about 49 inutes, and at 60 C is about 32 inutes to full discharge. It c an be seen the siilarity of the siulation and the experi ental result however at the final experient, the battery was broken as in Fig ure 6 then on the graph in Figure 5, at 60 C, the perforance of battery went down. 5. Conclusion Fro the discharge results of lead-acid battery 12 V 20 AH, the atheatical odel and th e experient have the siilarity. By atheatica l odel d ischarged current 20 A, 9. 6 V, the discharg ing tie of the battery at 25 C was 40 inutes and will also take longer tie at higher teperat ure. At the teperature 60 C, the discharging tie was 70 inutes. The experient of battery discharged current 20 A, 9.6 V, the discharging tie of the battery at 25 C was 40 inutes and will also take longer tie at higher teperature. At the teperature 45 C, the discharging tie was 55 inutes. However at teperature above 45 C, the battery was going to be broken. After 60 C experient, the battery was broken according to the teperature liitation shown as in Figure 6. Therefore even the battery capacity is longer when operates at higher teperature but the battery is able to stand only in the specific teperature. This study can lead to develop a suitable Battery Manageent Unit for PV syste. Figure 6. The broken battery after high teperature testing. 6. Discussions Al though the study results showed that the batte ry can work well whe n used at high teperatures however the battery should not be u sed at higher teperatures than its li itation beca use the battery will be destroyed at rated teperature [11-14], the result showed in Figure 6, co- this fired issue. REFERENCES [1] D. Linden and T. B. Reddy, Handbook of Batteries, 3rd Edition, M cgraw-hill, New York, [2] J. F. Manwell and J. G. McGwan, Lead Acid Battery Stor age Model for Hybrid Energy Syste, Solar Energy, Vol. 50, No. 5, 1993, pp doi: / x(93) [3] J. B. Copetti, E. Lorenzo and F. Chenlo, A General Battery Model for PV Syste Siulation, Progre ss in Photo- voltaics Research and Applications, Vol. 1, No. 4, 1993, pp doi: /pip [4] D. M ayer and S. Biscaglia, Modeling and Analysis of Lead Acid Battery Operation, 11 th International Telecounications Energy Conference, October, Vol. 2, pp. 23.3/1-23.3/6. [5] C. Arenta-Deu, Capacity Effects on the Deterination of the State-of-Charge in Lead-Acid Cells, Renewable Energy, Vol. 4, No. 2, 1994, pp doi: / (94) [6] M. Ceraolo and S. Barsali, Dynaical Models of Lead- Acid Batteries: leentation Issues, IEEE Transactions on Energy Conversion, Vol. 17, No. 1, pp [7] H. Bode, Lead-Acid Battery, John Wiley & Sons, New York, 1977, p [8] R. A. Jackey, A Siple, Effective Lead-Acid Battery Modeling Process for Electrical Syste Coponent Selection, The Math Works, Inc., Natick, doi: / [9] R. Jackey, Autootive Electrical Syste Siulation and Control, The Math Works, Inc., Natick, [10] N. Moubayed, J. Kouta, A. El-Ali, H. Dernayka and R. Outbib, Paraeter Identification of the Lead-Acid Batrd tery Model, 33 IEEE Photovoltaic Specialists Conference, Beirut, May 2008, pp [11] G. W. Vinal, Storage Battery, 4th Edition, John Wiley & Sons, New York, 1955, p [12] L. Seyonov, Storage Batteries Maintenance Manual, Mir, Moscow, 1967, p [13] D. Linden, Handbook of Batteries, 2nd Edition, McGraw- Hill, New York, 1995, pp [14] Dynasty Division, VRLA Battery Life Expectancy and Teperature, C&D Technologies, Inc., Blue Bell.