Battery state-of-charge

The determination of SoC can be based on the measurement of internal parameters (electrolyte or active mass parameters) or external parameters (temperature, voltage, current). The possible measurement methods are shown in Fig. 8.8. 

Internal battery parameters can only be measured by the use of speeial sensors [5], which leads to high costs. Most of the known methods are based on eleetrolyte measurements. According to the cell reaction of the lead-acid battery, the eleetrolyte is not only necessary for the ionic transport but is also necessary for the charge and discharge reactions. The ions of the electrolyte take part in the reactions. This results in a linear relation between the SoC and the ionic concentration of the electrolyte. Other electrolyte parameters vary approximately linearly with concentration. The relationship between acid rel. dens, and these other parameters is given in Table 8.2. 

For SoC measurements, it is possible to measure a representative electrolyte parameter e.g., measurement of buoyant force, refractive index, concentration, acid rel. dens, measurement by hydrostatic pressure, conductance, dielectric 

The rated or nominal capacity is the value for the Ah capacity given by the manufacturer at nominal operating conditions (defined by temperature, current, and end-of-discharge voltage). As a standard, the 10 h capacity (N = 10) should be used. A transformation between any temperature between 10 and 30°C and the nominal temperature is possible with the given equation. If the manufacturer only specifies values for the 100-h, 20-h, or 5-h capacity, then a rough approximation of the capacity can be gained from the rules-of-thumb  

The measured capacity is the capacity available at a capacity test with 7io down to 1.8V/cell (according to DIN 43539) starting at state-of- charge FULL at any time after taking the battery into operation. 

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A generalized controller operational flowchart is included in Figure 2. This flowchart shows relative battery state-of-charge (SOC) to be the starting criteria for the decision tree. SOC is defined as the ratio of ampere-hours (Ah) stored in the battery array at any given time to the maximum Ah capacity of the array. During this process the actual controller subroutine also includes the voltage and current that is available and/or required by each component. However, for the purpose of explanation, the power available or required by various system components can be related to battery SOC. 

Figures 3 and 4 depict the system performance of Case 1 for the first weeks of February and August respectively. In these plots the power produced by the PV array is shown along with the power requirement of the system load and battery state-of-charge (SOC). Figures 5 and 6 show system performance for the first weeks of February and August for Case 2, respectively.

Fig. 6.27 Experimental results obtained on the fuel cell power train in hard hybrid configuration for the R47 driving cycle a battery, input electric drive, and output DC-DC converter powers versus cycle length, b hydrogen, input and output DC-DC converter powers versus cycle length, c battery state of charge versus cycle length...

To compensate for the response of the fuel processor, a control architecture was developed to allow a battery system to provide for peak power demands. The power plant has been designed to maintain the batteries state of charge at an optimal level while the batteries provide the capacitance necessary to meet any load topography. In this configuration, the transient-following capabilities of the power plant are greatly enhanced. 

Aylor, J.H., Thieme, A., and Johnson, B.W. 1992, A battery state-of-charge indicator, IEEE Trans. Ind. Electr., 39 398-409. 

Pang S, Farrell J, Du J, Barth M (2001) Battery state-of-charge estimation. In Proceedings of the 2001 American control conference. (Cat. No.01CH37148), pp 1644—1649. IEEE, Arlington... 

Sabatier J, Aoun M, Oustaloup A et al (2006) Fractional system identification for lead acid battery state of charge estimation. Sig Process 86 2645-2657. doi 10.1016/j.sigpro.2006.02. 030... 

Cai CH, Ehi D, Liu ZY (2003) Battery state-of-charge (SOC) estimation using adaptive neuro-fuzzy inference system (ANFIS). In Proceedings of the 12th IEEE international conference on fuzzy systems, FUZZ 03, pp 1068-1073. IEEE... 

Lee Y, Wang W, Kuo T (2008) Soft Computing for Battery State-of-Charge (BSOC) Estimation in Battery String Systems. IEEE Trans Industr Election 55 229-239. doi 10.1109/ TIE.2007.896496... 

ABSTRACT We report on the microwave assisted hydrothermal synthesis of LiMnPO and LiCoPO and their electrochemical characterization by means of cyclic voltammetry and potentioelectrochemical impedance spectroscopy (PEIS/SPEIS). The influence of various synthesis parameters like pH-value and reaction time on the particle shape and size and thus on the electrochemical performance are studied. In addition, effects of the battery state of charge on the impedance spectra are investigated and discussed. 

Martinet, S., Durand, R., Ozil, R. et al. (1999) Apphcation of electrochemical noise analysis to the study of batteries state-of-charge determination and overvoltage detection. Journal of Power Sources, 83, 93-99. 

Battery systems are presently available for industrial trucks, easily recharged by new-generation control circuits that also permanently survey the batteries state of charge. 

Battery Behavioral Model for Real-Time Battery State-of-Charge Estimation... 

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