Project 2 Thermal modeling of battery pack
Modelling of battery pack:
The modelling of the lithium ion cells are done in the matlab with the help of the generic battery model.
In the above model we have 10 generic battery model connected in the series connection.The parametrs of all the cell remains the same.
The parameters of the battery is given above.The aging parameters are also shown.The initial age is assumed to be 0 and the initial state of charge is also set to 0.
The battery is charged and discharged through the controlled current source with a square wave generator.The amplitude of the square wave is set to the capacity of the battery to give 1C rate of charging and discharging.
The temperature effect of the cell is also need to be analysed.So a varying signal of temperature is given to the battery by a stair generator which is used to generate a varying signals over the period of time.For first 5 hrs the temperature is maintained at 25 and for next 3 hrs it falls to 10 and for the rest of the period it raises to 35.
The output of the battery is connected to the scope to view the soc ,voltage ,temperature and the age of the cells.
The simulation is run for 10 hours to see the charging and discharging effect of the cell along with the temperature values.
First the simulation is done for 1C rate of charging and discharging.The soc of the battery starts increase from 0 to 100 at hte time when the charging current rises from -5.4 to 5.4 A at 1C rate.After that the soc starts decreases as the discharging current starts to flow.The combined charging and discharge cycles correspond to the rise in the age of the cell.
The temperature of the cell remains in the value of 50 during the input temperature of 25 and when the temperature falls to 10 the overall temperature also falls and then rise to a peak value and when the temperature rise to 35 the overall temperature also rises to 60.The voltage follows the pattern of charge and discharge of the cell with the peak voltage at 8V.
Now the simulation done for 2C charging and discharging rate,It is done by changing the amplitude of the square wave generator.
When the charging and discharging is done at a faster rate the soc also reaches the full value at a faster rate and the age cycles are also drastically increasing leading to a unstable state of the cell.The temperature value is also seen to rise at a higher level when the flow of current is more.The voltage also rise to a peak value of 15V.
Now we can run the simulation at a lower C rate for charging and discharging.
When the charging and discharging is done at 0.5C rate the parameters seem to be halved from the parameters of 1C rate.The soc of the cell starts to charge to 50 and then starts discharge The temperature and the voltage follows the same pattern of 1C rate but the peak value will be lower than that of 1C rate.The peak voltage will be 7V.The age of the cell also reduces for one charge and discharge cycle thus improving the battery life time.