Project 2 Thermal modeling of battery pack

AIM

• To simulate the thermal effects and compare the life cycle performance of 10 cell series lithium-ion battery model at various temperatures, charge & discharge rates using MATLAB.

Here the inbuilt model Lithium-ion battery pack with fault is taken as the reference model and has been modified accordingly

reference model: https://in.mathworks.com/help/physmod/simscape/ug/lithium-ion-battery-pack-with-fault.html

Simulink model

•  the above model consists of 10 cells in series, where the first pack has 4 cells (cells 01-04). the second pack has only one cell (cell 5) which is fault one and the third pack has 5 cells (cells 6-10)

Blocks, parameters, and explanation

good cell packs (1-4 and 6-10 cells)

  

fault cell (cell 5)

  

• in the fault cell (5), the capacity, open-circuit voltage, resistance, and capacitance are altered.
• then to measure the temperatures of cells 4, 5, 10 the below modifications are done in the T subsystem of the above model

 

• then connected to scope by from blocks for observing the result.

CONDUCTION

• the heat transfer in the thermal network is done by conduction through a layer of material.
• this block conducts heat transfer between the cell packs ie. first (1-4 cells) and second pack (cell 5). then between the second (5) and third pack (6-10 cells)

Block parameter

 CONVECTION

• the heat transfer in a thermal network is done by the convection method due to fluid motion.
• in this model, the heat transfer is done from the ambient thermal source to cell packs

 

• the ambient temperature is measured by the temperature sensor and displayed

 SOC

• the values from the current sensor are integrated and then connected to the gain block, add block, and then to the scope

Cyclic charge/discharge profile

•  AC current source block is used for the charge/discharge cycle 

Simulation and Results

case 1: when ambient, cell packs temperature are the same 293 K. the current peak amplitude in the AC source block = 50 A

Temperature

• Initially, all the packs start with 293 K
• according to the charge/discharge cycles, the temperature of the packs are varied
• we can observe that cells 4 and 10 follow the same pattern reaching a maximum temperature of 325 K
• the faulty cell 5 shows a different pattern and reaches a maximum temperature of 336 K which will impact the overall performance of the total battery pack.

SOC

• here one charging+discharging cycle takes 600 sec
• with a current peak amplitude of 50A, SOC varies from 0 - 70 %

CONDUCTION (cell 4-5)

  

• here the heat conduction and temperature difference between the (first pack) cell 4 and (second pack) cell 5 are plotted.
• the heat conduction during charging is around -12W and during discharging is around -22W. 
• the negative sign indicates the heat transferred (direction) from cell 5 to cell 4. since cell 5 had a higher temperature due to the fault conditions.
• the temperature difference during charging is around -6K and during discharging is around -11k

cell 5-6

  

• here we can observe positive values since the heat transfer direction is from cells 5 - 6
• the heat conduction during charging is around 24W and during discharging is around 15W
• the temperature difference during charging is around 12K and during discharging is around 7K

CONVECTION (heat transfer through molecules of gases and liquid)

Ambient - cells 1-4

  

• at the end of the simulation, the heat convection is about -68W and the temperature difference is about -32K

Ambient - cell 5

  

• at the end of the simulation, the heat convection is about -21W, and the temperature difference is about -41K

Ambient - cells 6-10

   

• at the end of the simulation, the heat convection is about -80W and the temperature difference is about -32K

the temperature difference is different with ambient-cell 5 when compared to the others

charge/discharge cycle:

  

• we can observe the current values varying from -50 to 50 A (charging/discharging)
• the voltage varies from 30 to 43 V

case 2: when ambient temp = 300K, cell 1-4 = 295K, cell 5 = 320K, cell 6-10 = 310K, and the current peak amplitude in the AC source block = 40 A

Temperature

• Initially, cell4 starts at 295K, cell5 starts at 320K, cell 10 starts at 310K
• we can observe that at 2000 sec, cells 4 and 10 are temperature balanced and follow the same pattern reaching a maximum temperature of 320 K
• the faulty cell 5 shows an initial decrease and raises to a maximum temperature of 326 K.

SOC

• here one charging+discharging cycle takes 600 sec
• with a current peak amplitude of 40A, SOC varies from 0 - 55 %

CONDUCTION (cell 4-5)

  

• here the heat conduction and temperature difference between cell 4 and cell 5 are plotted.
• the heat conduction during charging is around -9W and during discharging is around -14W. 
• the temperature difference during charging is around -4K and during discharging is around -8k

cell 5-6

  

• the heat conduction during charging is around 15W and during discharging is around 9W
• the temperature difference during charging is around 8K and during discharging is around 4K

CONVECTION (heat transfer through molecules of gases and liquid)

Ambient - cells 1-4

  

• at the end of the simulation, the heat convection is about -41W, and the temperature difference is about -21K

Ambient - cell 5

  

• at the end of the simulation, the heat convection is about -13W, and the temperature difference is about -26K

Ambient - cells 6-10

  

• at the end of the simulation, the heat convection is about -52W and the temperature difference is about -20K

the temperature difference is different with ambient-cell 5 when compared to the others 

charge/discharge cycle:

  

• we can observe the current values varying from -40 to 40 A (charging/discharging)
• the voltage varies from 31 to 42 V

Using UDDS current profile

• the UDDS current profile is given as drive cycle input through a controlled current source
• the SOC here is initially considered as 1
• all the ambient, cell packs temperature are the same 293K
• the simulation time is 1400 sec

Input signal builder

Simulation and Result

Controlled current source

  

• the current profile matches the UDDS cycle. negative current indicates charging and positive current indicates discharging
• the voltage varies between 35.5 to 37 V

Temperature

• Initially, all the packs start with 293 K
• according to the UDDS current profile, the temperature of the packs are varied
• we can observe that cells 4 and 10 follow the same pattern while cell 5 is different due to the fault condition
• cell 5 achieves a higher temperature than the others

SOC

• for the UDDS current profile, SOC is reduced to 94%

CONCLUSION

• the thermal modeling of 10 cell series lithium-ion battery model for various temperatures, charge/discharge profiles are simulated.
• the results for temperature, SOC, conduction, convection, current, voltage are plotted, analyzed, and explained.

Gdrive attachments: https://drive.google.com/file/d/1XdBj9pbvuSZY2mmeQt60-1w7Cdplds8w/view?usp=sharing