Project 2 Thermal modeling of battery pack

THERMAL MODELING OF BATTERY PACK

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.

Introduction:

The lithium-ion batteries are widely used as energy source in different hybrid and electric vehicle,however the operatiom characteristics of the battery in such vehicle are strongly dependent on the operation temperature and therefore, with purpose to improve these characteristics a good thermal control system should be utilized.

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

So, for 10-cell series lithium ion battery here I used MATLAB simulink for finding thermal effect and life cycle performance related to temperature,charge and discharge.

Lithium-ion battery pack fault is to simulate a battery pack consisting of multiple series connected cell in an efficient manner. It also show how a fault can be introduced into one of the cells to seee the impact on battery performance and cell temperatures. For efficiency identical series-connected cells are not just simply modelled by connecting cell model in series. Instead a single cell is used and the termal voltage scaled up by the number of cells. The fault is represented by charging the parameters for the cell 5 fault subsystem reducing both capacity and open - circuit voltage and increasing the resistance values.

A default MATLAB Simulink model of battery pack which I used for 10 - cell battery pack thermal modelling.

In this project will simulate the thermal effect of a 10S1P lithium - ion battery pack, which consist of 10 ANR26650M1-B High -performence nanophosphate lithium iron phosphate (LiFePO4) battery technology delivers high power and energy density combined with excellent safety performance and extensive life cycling in a lighter weight, more compact package. To make its interesting, a fault has been introduced in one of the cell to demonstate the effect of the faulty cell on the entired pack.

ANR26650M1-B Nanophosphate lithium ion phosphate (LiFePO4) datasheet used for this project:

What is Faulty Cell?

A faulty cell demonstates performance that is different than the other cell usually most cell will be displaying the same SOC , temperature voltage level etc. But a faulty cell will show sign of overheating,faster dischagre (due to reduced capacity or reduced OCV) oe will be unbalanced cell. thiss will be impact the performance of the entire pack as the faulty cell will limit the pack from itilizing its maximum potential.

In this project the faulty cell is representing by adding an extra external resistor. this will make the cell react diffirently then the other cells.

Simulink Model:

• In this model 1st we give UDDC current profile to battery pack with help of signal builder block. and import the UDDS datas. change the axes time.
• UDDS cycle (current vs time) has been used to charge discharge the batteries for given periode of time 1369 sec.
• There is three module have been connected together is series to make a 10 cell battery pack model.
• In Cell number 6 resistor can be added to vary the rate of discharge.
• All cell are configure same as ANR26650M1-B cell. It means put same value which in datasheet .
• All cel are initially at 25 degree c. A temperature source is used to test the cell performance at 3 different temperature, like at 25 degree celsius , At 45 degree celsius , At -10 degree celsius.
• convective and conductive block has been added for heat transfer between blocks.

Vehicle current model:

• In vehicle current requirement subsystem block ,the signal builder block used to apply UDDS current profile and simulink-ps converter block is used to convert the simulink siganl to physical signal. Connecting port block used to output the signal.

UDDS Current Profile in signal Builder:

Module 1 [Cell 1-5]:

• In this module we used the 5 table based battery block in which we put the datasheet value on it. Here i put the battery specification like, 2.5Ah capacity, initial temperature value is 298K etc. And this 5 cell are connected in series.
• Also here we use the conductive heat transfer block in which we put the thermal conductivity is 401 W/(K*m), Area is 10 m^2 , and thickness is 0.1m.
• Here we use for convective heat transfer block in which we put the heat tranfer co-efficient is 20 w/(K*m^2), area is 10 m^2.and one end of this block is connected to thermal source and other is connected to perticular cell.
• Here we use perfect insulator also.
• here we use temperature sensor to sense the themperature of cell and display the value in scope. and one end connected to thermal reference.
• SOC of every cell is also calculate by using add and gain block , and display the SOC value in % in display block.

Module 2 [Cell 6]:

• In this module we used the table based battery pack block in which we put the datasheet value on it. Here i put the battery specfications like, 2.5Ah capacity, initial temperature value is 298K etc. And addition to that accross the battery terminal we use the 5 ohm resistor to shows the this is the faulty cell.
• Also here we use the conductive heat transfer block in which we put the thermal conductivity is 401 w/(K*m), Area is 10 m^2 , and thickness is 0.1m.
• Here we use the convective heat transfer block in which we put the heat transfer co-efficient is 20 W/(k*m^2), Area is 50 m^2 and one end of this block is connected to thermal source and other is connected to perticular cell.
• Here we use the perfect insulator also.
• Here we use temperature sensor to sense the temperature of cell and display the value in scope and dashboard. Also it one end connected to thermal reference.
• And SOC of every cell is also calculate by using add and gain block, and display the SOC value in % in display block.

Module 3 [Cell 7-10]:

• In this model we used for the 4 table based battery block in which we put the datasheet value on it. Here i put the battery specification like, 2.5Ah capacity , initial temperature value is 298K ect. and this 4 cell are connected in series previous 1 and 2 modules are follow same procedure and battery specifications.
• Also here we use the conductive heat transfer block in which we put the thermal conductivity is 401 w/(k*m), area is 10 m^2 and thickness is 0.1m.
• Here we use the convective heat transfer block in which we put the heat transfer co-efficient is 20 W/(k*m^2), area is 10m^2 and one end of this block is connected to thermal source and other is connected to perticular cell.
• Here we use perfect insulator also.
• Here we use temperature sensor to sense the temperature of cell and display the value in scope and dashboard. also it one end connected to thermal reference.
• SOC of every cell is also calculate by using add and again block, and display block.

SOC Calculation Model:

• Here we use the 3 goto block and 3 from block and scope to analyze the change in SOC of 3 different cell module.

Temperature Calculation Model:

• Here we use the 3 goto block and 3 from block and scope to analyze the change in temperature of 3 different cell modules.

To incorporate for the positioning of this cell (center of pack) certain changes have been made:

• The convective area is 10m^2 for the remaining 9 cell, but has been increased to 50m^2 here.
• The ambient temperature provided from temperature source to the remaining 9 cell are the same 298K, but has an increament of 305K for this cell. Its means 305K.

Result:

A] At 25°C (298k)

1] SOC Of different Module [%]:

• Model 2 has a much steeper slope than the other modules because 6 ohm resistors. A load (in the form of resistor) with a resistance of just 6 ohm will draw in more current compared to no added load. which means greater rate of discharge and hence more drainage of SOC.
• module 1 SOC cell1-5= 91.22 %, temp cell 1-5 = 298.15 k
• module 2 SOC cell 6 = 82.9 % , temp cell 6 = 298.2 k
• module 3 SOC cell 7-10 = 91.23 % temp cell 7-10 = 298.22k

2] Temperature change in module (k):

• initial temperature of battery pack is set to 298k.
• module 2 starting time period lowly increaseing the temperature due to resistance value.
• ambient temperature supplied is 298k. and reache the 298.22 k.

B] At 45°C:

1] SOC of different module [%]:

• model 2 has a much steeper slope than the other because of added 6 ohms resistor. A load with a resistor just 6 ohm will draw in more current compared to no added load. Wich means greater rate of discharge and hence more drainage of SOC.

2] Temperature change in module(K):

• Initial temperature of battery pack is set to 298k.
• although ambient temperature supplied is 45 degree celsius.
• module 1 SOC cell1-5= 91.22 %, temp cell 1-5 = 318.15.15 k
• module 2 SOC cell 6 = 82.22 % , temp cell 6 = 318.12 k
• module 3 SOC cell 7-10 = 91.2 % temp cell 7-10 = 318.1k

C] At -10°C:

1] SOC of different module [%]:

• Model 2 has a much steeper discharge slope than the other because of added 6 ohm resistor.A load (form of resistor) with a resistance of just 6 ohm will draw in more current compared to no added load. which means greater rate of discharge and hence more drainage of SOC.

2] Temperature change in module (K):

• Initial temperature of battery pack is set to 298k.
• Ambient temperature supplied is 263.15 k (-10 degree celsius).
• module 1 SOC cell1-5= 91.23 %, temp cell 1-5 = 263.15 k
• module 2 SOC cell 6 = 82.15 % , temp cell 6 = 263.22 k
• module 3 SOC cell 7-10 = 91.24% temp cell 7-10 = 263.22k

Conclusion:

MATLAB model for lithium ion battery pack of 10 cell series connection has been created. The thermal effects on the battery pack has been simulated . From the observation of model we have created it can be say that, when the temperature value increases then its respective charging and discharging capacity decreases due to the heat generated in the batteries.

To observe this charge we have simulated the model for two different temperature , so it can be obsreved that there is a decreases in the %SOC when the temperature value is increased. For the efficient operation of the battery pack, proper thermal management is required.