Week 7 State of charge estimation
Coulomb Counting:
The Coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC. Coulomb counting method is done to estimate the soc which is estimated from the discharging current, , and previously estimated SOC values.
To improve the Coulomb counting method, a new technique called modified Coulomb counting method is proposed. The modified Coulomb counting method uses the corrected current to improve the accuracy of estimation.The corrected current is the function of discharging current. There is a quadratic relationship between the corrected current and discharging current of battery.
Coulomb Counting for SOC estimation by implementing BMS:
With technological advances, electronic systems become widely used in most applications especially in multimediaones. These systems require to be powered permanently. Toensure that energy supply, there are specific power systemswhich are rechargeable batteries. Indeed they are differenttypes of rechargeable batteries, which differ from each other by several characteristics, such as the chemical compositions,the energy density and their lifetime [1,2]. Besides these portable electronic devices tend to be more and more compactand lighter. Batteries based on Lithium-Ion (Li-Ion)technology seem to be the more adequate thanks to their goodcharacteristics like high energy density, high voltage,important number of charge/discharge cycles and security.
Accuracy in SOC knowledge can avert batteries fromcoming in over-charge and deep-discharge and these statesmay cause irreversible damage to the battery’s internalstructure [4].In literature, many methods were proposed for the batteriesSOC estimation [5-6]. In fact three main types of methods areidentified: electrochemical methods, electrical methods andadaptive ones. The electrochemical methods in spite of theirhigh accuracy are judged difficult to implement neither onsoftware nor on hardware solution because of the need toaccess to the chemical structure of battery [7, 8]. Adaptivemethods [9] require an equivalent model and a resolutionalgorithm such as neural network [10], Kalman filter [11],fuzzy logic algorithm [12] and state observers [13]. Soaccuracy of these methods depends on the efficiency of the battery model. Unlike previous methods, electrical onesrequire only parameters that are obtained by measurementssuch as terminal voltage, current and internal resistance.Among these electrical methods, coulomb counting based oncurrent integration remains one of the most widely usedmethod due to its implementation simplicity and lowcomplexity [8, 7, 14,15].In this paper the purpose is to propose an accuratemonitoring solution for multimedia applications, which can provide an accurate SOC indication and provide insight on the battery health in order to ensure a best use of the Li-Ion battery during their lifetime. The overall project includesespecially two steps. In the first one we implement a coulomb-counting algorithm for SOC estimation. In the second step weaim to propose a battery model and an adaptive algorithm toenhance the accuracy.
This paper suggests a SOC estimation method for Li-Ion batteries on the basis of coulomb counting algorithm. Thismethod characterizes the operating states of a Li-Ion battery(charge, discharge, self-discharge) and tends to overcome thelimitations of the classic coulomb counting method such as thecumulative errors, the aging and temperature effects on theaccuracy of the battery state of charge estimation. The proposed algorithm has been implemented on an embedded platform based on the microcontroller PIC18F developedwithin IntelliBatteries Company as a demonstrator andvalidated by simulation and experimental tests.In the next section we introduce the coulomb countingmethod and the basics of the different steps of the algorithmand we explain how we overcome the ageing and thetemperature effects. In the third section we describe theimplementation process on the hardware platform as well asthe experimental tests.
Li-Ion Batteries requires a specific charge method whichconsists on the constant current-constant voltage (cc-cv)charging algorithm illustrated. Also these batteriestype have specific behaviors such as the different dischargegaits under different currents shown in and the self-discharge characteristic.So battery monitoring is one of themost important challenges facing Li-Ion batteries in order tomonitor these behaviors. State-of-charge (SOC) estimation isthe crucial task in battery monitoring.
