Week 7 State of charge estimation

Coulomb counting method :-

Coulomb counting method is uesd to measure the dischrging current of a battery and the integrate the

discharging current over time in order to estimate SOC. coulomb counting method is done to estimate the

SOC(t) ,which is estimated fromthe discharging current I(t), and previously estimated SOC values SOC (t-1)

SOC is calculated by follwing equation:-

SOC (t)= SOC(t-1)+ I(t)/Qn*deltat.

where,

SOC(t)= state of charge

I(t)= Discharging current

Qn= Battery capacity.

State of charge is one of the important parameter of battery which defined as ratio of current capacity to the nominal capacity.The various mathematical method of estimation are classified according to methodology. there different method are use to estimated SOC are as follows:-

1. Direct measurement :- This measurement uses a physical property of battery such as voltage and impedance of battery. the direct method consist of different methodas are as follows:-

i)Open circuit voltage method.

ii)Terminal voltage method.

iii) Impedance method.

iv)Impedance spectroscopy method.

2. Book keeping estimaton:- These method uses a discharging current as the input and integrates the discharging current over the time to calculate the SOC. this method is consist of various method:-

i)Coulomb counting method.

ii) Modified coulomb counting method.

3. Adaptive system:-The adaptive system are selfdesigningand can automatically adjust the SOC for different discharging conditions . It consist of diffreent method such as:-

i) BP Neutral Network.

ii)RBF Neutral Network

iii)Fuzzy logic method.

iv)Fuzzy neutral network.

v)Support vector machine.

vi) Kalman filter.

4. Hybrid methods :- hybrid models benefit from advantage of each SOC estimation method .the hybrid method generaally produce good estimation of SOC compared to individual method .this hybrid method include the different method for SOC estimation:-

i)Coulomb Counting and EMF combination.

ii)Coulomb Counting and Kalman Filter combination.

iii) Per-unit system and EKF combination

Battery management system implement for harness dashboard:-

In this model BMS system is implement by using the coulomb counting method along with suitable algorithm. In this case the coulomb counting method is design by using simulink in battery managementsystem .In these model the SOC estimation by using coulomb counting and EKF ( Kalman filter) method.

This is an coulomb counting method for SOC estimation used in BMS system in the model:-

In the battery management system the coulomb counting method can be implement by using a suitable algorithm. the flow chart gives a idea about SOC estimation work:-

Report on test result on test :-

1) The result include the cell voltage, pack current, cell temperature, SOC. After running the simulation at some time the cell voltage changes different value according to drive cycle.

2)The pack current waveform is the combination of drive cycle .In this pack current negative current indicate the discharging state and the regenerative breaking charging battery while in driving condition and it indicate bypositive current.

3)During this driving condition the cell temperature increase gradually. Their are different wave in cell temperature because cell temperature depend upon poisition and configuration of various cell in battery.

4)As per simulation , Initially the SOC is 70 upto 75% .After some cycle it discharge and it get reduced and the SOC having different wave because the SOC calculated by two method coulomb counting method and EKF .

5)When considering charging condition by the CC charging the cell voltage start to increase and it become constant at CV charging but CV charging take a more time than the CC charging. When we see constant current charging at time SOC will increase constantly.