Project 2 Thermal modeling of battery pack

OBJECTIVE : For a 10 cell series lithium ion battery model, simulate the thermal effects and compare life cycle performance at various temperatures, charge & discharge rates using MATLAB.

SOLUTION : Lithium ion batteries are widely used as energy sources in different hybrid and electric vehicle. However the operation characterstics of the battery in such a vehicle are strongly dependent on the operational temperature and driving cycle.

The temperature of lithium battery is important for its performance, efficiency, safety and capacity and is influenced by the operational temperature and by charging and discharging the process. Therefore a thermal model of the battery is used in order to estimate the cell temperature and life cycle of it.

For 10 cells of lithium ion connected in series is shown below :-

Now going for the block parameters :-

Above blocks represent the parameterization of battery block and square wave generator block

In Sq wave block amplitude is taken equal to rated capacity for C-rate charge and discharge of battery.

Frequency is taken as 3600 to make the cycle equal to 1hr.

Run time is kept for 3600*5 i.e. equal to total 5 cycles.

Now running the model for 5 cycles we get :-

• Here we can see that square wave signal and current values are equal to 5.4 Ah.
• Total 5 SOC cycles have been taken place
• In 5 cycles aging of battery is almost equal to 2.5
• And the cell temperature is almost equal to 48 Deg C.

CASE 1 :- Increasing the temperature to 35 from 20 and now observing its effect on model.

• As the temperature increases to 35 Deg C and by keeping other parameters same we observe that aging of cell increases to = 3.5 and the temperature rises to 65Deg C.

CASE 2 :- Now changing the charging and discharging rate by 2C as increasing the amplitude to 10.8 from 5.2 in square wave generator we get :-

• As by increasing the charging and discharging rate by 2C have affected the aging and temperature of the cell.
• Aging of cell is around 7.5 and the cell temperature has reached approx to 80 Deg C

CASE 3 :- Now changing the charging and discharging rate by 0.5C as reducing the amplitude to 2.7 from 5.4 in square wave generator we get :-

• As by reduced the charging and discharging rate by 0.5C have affected the aging and temperature of the cell.
• Aging has been limited to arround 1 and temperature is also equal to 35 Deg C

RESULT : From CASE 1,2 & 3 we have observed that :-

• Case 1 : As the simulation temperature increases it will age the battery cell at a faster rate and the cell temperature will increase too.
• Case 2 : As we increase the charging and discharging rate by 2C it will age the battery cell at much faster rate and the cell temperature will be highest.
• Case 3 : As we decrease the charging and discharging rate by 0.5C it will age the battery cell at much slower rate and the cell temperature will be minimum.