Week 7 State of charge estimation
Coulomb counting:
Coulomb counting is a technique used to track the state of charge of a battery pack.
It works by integrating the active flowing current (measured in amps) over time to derive the total sum of energy entering or leaving the battery pack.
This produces a capacity that is typically measured in Amp-hours.
BMS:Battery management system:
1.The elctric vehicle manufacturer uses large amount of batteries pack to gether to get the required power for the movement of the vehicle.
2.Though these batteries pack in a lot of punch for its size they are highly unstable in nature.
3.It is very important that these batteries should never be over charged or under discharge at any circumstance which brings in the need to monitor its voltage and current.
4.This process gets a bit tougher since there are a lot of cells put together to form a battery pack in EV and every cell should be individually monitored for its safety and efficient operation which requires a special dedicated system called the Battery Management System.
5.Also to get the maximum efficiency from a battery pack, we should completely charge and discharge all the cells at the same time at the same voltage which again calls in for a BMS.
6.The BMS helps in estimating the state of charge of the batteries (SOC).
7,There are different types of SOC state of charge estimating techniques.They are
a)Voltage method
b)hydrometer
c)Coulomb counting
d)Impedance spectroscopy
8.Let us discuss about the Coulomb counting method
To determine available capacity, coulomb counting relies on the integration of the current drawn from and supplied to a battery over time, τ∈t0t">τ∈t0t, as given by
`SOC(t)=SOC(t0)-int_0^t (eta(T)*I(T))/(Cb)*dt`
where I is the current and η is the efficiency during charge and discharge operations .
9.Coulomb counting is advantageous in terms of a simple structure and its ease of implementation.
limitations:
10.However, some problems make it difficult to accurately estimate battery SOC by coulomb counting.
11.Because battery capacity and efficiency are significantly influenced by operating temperature and current direction, these factors should be considered to correct for battery SOC.
12.Sensor accuracy is also important because accumulated errors can lead to a drift in the estimated battery SOC.
13.Furthermore, one of the main problems in coulomb counting is that it is necessary to calibrate the initial battery SOC. `
solution:
14.To over come the above problems BMS plays an very important to measure and control the battery temperatures and over charging and discharging of the battery can be maintained
15.The basic structure of the BMS is
16.The battery management system is used to control each and every cells voltage current and temperature which helps in bettery estimating the state of charge of the battery