Week 7 State of charge estimation
The answer to the question is attached in PDF format below from google drive.
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COULOMB COUNTING
The coulomb counting method is useful for state-of-charge (SOC) estimation of lithium-ion batteries with high charging and discharging efficiencies. The charging and discharging characteristics are investigated and reveal that the coulomb counting method is convenient and accurate for estimating the SOC of lithium-ion batteries.
It uses the in and outflow of current to measure the SOC. It is measured by the equation
Q=SOCo+(INT(u=0 to v=T0+T)I(t)dT)/Q
Coulomb counting is attained through multiplying current entered or left the battery into the time is taken for it. Its unit is Amp-hour (Like as unit of charge)
Battery Management System
Battery management System protects, monitors, and optimizes the battery during the service life. Its functions are:
- Monitor
- Energy recovery
- Thermal management
- Computation
- Communication
- Protection
- Optimization
Coulomb Counting in Battery Management System.
It is done through certain pathways which are shown below.
Explanation: As the unit starts, the BMS monitors the Voltage and current of the battery, then assumes the initial current as zero.
But self-discharge also possible it has to be compensated, another two pathways are also possible one is Discharge pathway and the other is the Charging pathway. During the discharge pathway, the DOD is calculated since discharge is taking place then it is calibrated to the empty state.where as during the charging pathway SOC is calculated by the above formula, and it is calculated as done in the previous method.
The results of three of the pathways are communicated to the SOC indicator.
Other ways of SOC estimation.
- Voltage method
This method is easy but may contain a huge number of errors because temperature and materials affect the voltage value. Hence it is very unpractical.
- Hydrometer
It offers an alternative to measure SOC. When Lead-acid battery accepts charge its specific gravity increases. After discharge Sulphuric acid becomes light and hence the weight difference gives the SOC>
- Impedance spectroscopy
Spectro complex modeling method also can be used to measure SOC