Battery state determination

In general, there are two different architectures for BMSs namely, decentralized systems and centralized systems. These two architectures are illustrated for an electric vehicle (EV) application in Fig. 8.3 (decentralized) and Fig. 8.4 (centralized). In the decentralized system (Fig. 8.3), the individual BMS tasks are located in different devices. The charge control is part of the charger, the discharge control is part of the EV drive system, the battery state determination is carried out within a range meter, and so on. Some BMS tasks must be implemented in more than one device, especially in the case of safety management. Normally, there is little or no communication between the devices, so an optimized operation is not possible. Another disadvantage is that the battery-relevant control functions are located in different devices. Thus, each device must be adapted to the particular battery used. 

Cost The cost of the battery is determined by the materials used in its fabrication and the manufacturing process. The manufacturer must be able to make a profit on the sale to the customer. The selling price must be in keeping with its perceived value (tradeoff of the ability of the user to pay the price and the performance of the battery). Alkaline primary Zn—MnOz is perceived to be the best value in the United States. However, in Europe and Japan the zinc chloride battery still has a significant market share. In developing countries, the lower cost Leclanche carbon—zinc is preferred. Likewise, lead acid batteries are preferred for automobile SLI over Ni—Cd with superior low-temperature performance but with a 10 times higher cost. 

The actual battery state is mainly influenced by the historical operation of the battery. Therefore, methods for SoC determination should ideally take into account the history of the battery. Such (long-term) methods include simple charge balance and more complex adaptive methods. 

Statistical analysis is often used to determine differences between battery cells. If no charge-equalizing equipment is installed, the current through each cell is equal. Therefore, the cell/block voltages can be compared to estimate differences between cells. It is known that the voltage is not a direct indication of the battery state. Voltage can be used for relative analyses, however, and can show the changes of one cell in comparison with others. 

In order to ensure proper SoC indications, a periodic calibration is necessary. This can be done by fully charging or discharging the cell, so that the battery state is well determined and the SoC coimter can be reset. 

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. 

An emerging application for large quantities of Li-ion cells is the electrification of power trains, where Li-ion cells seem to be a proper technology which covers a broad spectrum of e-mobility applications like hybrid electric vehicles, plug-in hybrid electric vehicles and electric vehicles. For these applications a precise state determination of the Li-ion battery and its cells is mandatory to ensure a reliable operation of the vehicle. 

A key element in management of hthium batteries is the accurate and reliable determination of battery state-of-charge (SOC), whether or not the "history" of the battery is known from date of manufacture. Rehable SOC measurements are critical for many devices. Well-known interrogation techniques used to measure battery SOC include coulomb counting [11], voltage recovery [12], and electrochemical impedance spectroscopy (EIS) [13]. Often, these approaches yield data that is highly nonlinear, complex, or intractable, especially for rechargeable battery systems. 

P. Singh, Y.S. Damodar, C. Fennie, and D.E. Reisner, "Fuzzy Logic-Based Determination of Lead Acid Battery State-of-Charge by Impedance Interrogation Methods"Procs. EVS-17, Montreal, Canada, Oct 15-18, 2000... 

Tye [38] explained that separator tortuosity is a key property determining the transient response of a separator (and batteries are used in a non steady-state mode) steady-state electrical measurements do not reflect the influence of tortuosity. He recommended that the distribution of tortuosity in separators be considered some pores may have less tortuous paths than others. He showed mathematically that separators with identical average tortuosities and porosities can be distinguished by their unsteady-state behavior if they have different distributions of tortuosity. 

However, there is one exception to using the TCLP to identify a waste as hazardous. The DC Circuit Court, in Association of Battery Recyclers vs. U.S. EPA, vacated the use of the TCLP to determine whether manufactured gas plant (MGP) wastes exhibit the characteristic of toxicity. As previously stated, the TCLP replicates the leaching process in municipal landfills. The court found that U.S. EPA did not produce sufficient evidence that co-disposal of MGP wastes from remediation sites with municipal solid waste (MSW) has happened or is likely to happen. On March 13, 2002, in response to the court vacatur, U.S. EPA codified language exempting MGP waste from the toxicity characteristic regulation. 

Graphical Approach to the Analysis of Batteries of Stirred Tank Reactors Operating at Steady State. Even in reaction systems where it is not possible to determine the algebraic form of the reaction rate expression, it is often possible to obtain kinetic data that permit one to express graphically the rate as a function of the concentration of one reactant. Laboratory scale CSTR s are particularly appropriate for generating this type of kinetic data for complex reaction... 

FICs are useful as electrochemical sensors, electrolytes and electrodes in batteries and in solid state displays (Farrington Briant, 1979 Ingram Vincent, 1984). If a FIC material containing mobile M ions separates two compositions with different activities of M, a potential is set up across the FIC that can be related to the difference in the chemical activities of M. By fixing the activity on one side, the unknown activity on the other can be determined. This principle forms the basis of a number of ion-selective electrodes LaFj doped with 5% SrF2 is used for monitoring fluoride ion concentration in drinking water. Similarly, calcia-stabilized-zirconia is used in cells of the type... 

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