Challenge

Project 2 Thermal modeling of battery pack

SSujoy Dutta5 Jan 2022

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.

This example shows how to simulate a battery pack consisting of multiple series-connected cells in an efficient manner. It also shows how a fault can be introduced into one of the cells to see the impact on battery performance and cell temperatures. For efficiency, identical series-connected cells are not just simply modeled by connecting cell models in series. Instead a single cell is used, and the terminal voltage scaled up by the number of cells. The fault is represented by changing the parameters for the Cell 10 Fault subsystem, reducing both capacity and open-circuit voltage, and increasing the resistance values.

The example consists of a Simulink model with 10 cell connected in series. The model also shows how fault can be introduced into one of the cell to impact battery performance and cell temperatures. For efficiency, identical series cells are not used rather single cells are used and the terminal voltage is scaled up by number of cells. The fault is represented by changing parameters for cell 5 subsystem reducing capacity and open circuit voltage and increasing resistance values.

Following connections were made,

10 lithium ion batteries are connected with a combination of 3 packs. 1^st pack consists of 4 cells connected in series. 2^nd pack consists of cell 5 with fault designed to study the effect of temperature changes within the battery. 3^rd pack consists of five cells connected in series.
The heat transfer is observed between the pack by conduction and convection block used as modes of heat transfer
T subsystem is attached in between every pack to plot the temperature graph of the particular cell of that battery pack.
This battery pack is connected to AC current source for cyclic charge and discharge rate graph.
Current sensor is added to calculate the SOC of the battery

Cells 1 to 4 subsystem

The subsystem consists of a thermal model and lithium cell 1RC block which calculates the temperature and the thermal effect for cell and overall calculate for the battery pack.

Blocks inside the subsystem are gain block used to multiply the input signal by a constant i.e., u*gain. The other block are voltage sensor block and current- voltage source.

The voltage sensor block represents an ideal voltage sensor measuring voltage between any electric connection and converting it physical signal proportional to the voltage.

The current -voltage source represents an ideal voltage source capable of maintaining the specified voltage at its output regardless of the current passing through it. The output voltage is V=Vs where Vs represents the numeric value at the physical signal port.

Thermal Model: -

The thermal reference block represents the thermal reference point in a thermal network where the temperature is equal to absolute zero.

Controlled heat flow source: This block represents an ideal energy source in a thermal network that can maintain a controlled heat flow regardless of temperature difference. The heat flow rate is set by signal port SA positive heat flow rate flows from port A to B

Thermal Mass.: this block models internal stored energy in thermal network. The rate of temperature increase is proportional to heat flow into the material and inversely proportional to mass and specific heat of the material.

Temperature sensor. This block measures temperature in thermal network. There is no heat flow through the sensor. The physical signal port T reports the temperature difference across the sensor. The measurement is positive when temperature at port A is greater than at port B.

Lithium cell 1RC subsystem

This block consists of capacitance value depending upon the external physical signal input SOC and T. It is assumed that capacitance value is slowly varying over time and hence the equation i=C*dv/dt holds.

Resistance value R table depends upon external physical signal inputs SOC and T.

Voltage value EM which implements the cell main branch voltage source and determines value for capacity and state of charge. The defining equation depends upon cell temperatures.

Thermal Behaviour

Lithium ion cell RC branch equivalent circuit detail for 10 cells.

For cell 1 to 4

For cell 5

For cell 6 to 10

Amplitude for cyclic charge and discharge is set to 50A.

Temperature Source: This block represents an ideal energy source in a terminal network that maintain constant output temperature at port regardless of heat flow rate.

The block is used for convective heat transfer set to 299.1 K

Convective heat transfer:

The block models heat transfer in a thermal network by convection due to fluid motion.The rate of heat transfer is proportional to the temperature difference, heat transfer coefficient, surface area in contact with the fluid.

Conductive heat transfer : This block models heat transferrin a thermal network by conduction through a layer of material. The rate of heat transfer is governed by fourier law and is proportional to temperature difference, material thermal conductivity, are normal to heat flow direction and inversely proportional to layer thickness.

For SOC calculation

RESULTS: - Simulation-based on different temperatures

Test	Cell 01-04 Temp	Cell 05 Temp	Cell 06- 10 Temp
Test 1	299.1	299.1	299.1
Test 2	310	299.1	310
Test 3	310	320	330
Test 4	330	320	300
Test 5	310	350	310

1. TEST 1-EQual Temperatures:

All 3 cells have the same temperature at the start which is 299.1K. But in the beginning few seconds of simulation cell, no 5 oscillates with more than cell 4 and 10 because its design with fault and ranges to a higher temperature than cell 4 and 10. The temperature line of cell 5 unfollows cell 4 and 10 as cell 5 is designed with faults and ranges higher temperatures than other cells. Cell 10 has a higher temperature than cell 04 after 1300 seconds despite having more number of cells.

the SOC graph following the sinusoidal waveform and fluctuating after 297 seconds .

Conduction:

Cell 04-05

From the graph, we can observe that the heat transfer coefficient is 21.23 W/(m^2K)

and thermal conductivity is 10 W/mK

Cell 05-06

Heat transfer coefficient: 20.12W/m^2K

Thermal Conductivity: 10.06W/mK

Convection:

Heat transfer coefficient: -70.86 W/(m^2K)

Thermal Conductivity: -15 W/mK

Heat transfer coefficient: -13.41W/(m^2K)

Thermal conductivity: -26.07W/mK

Charge and discharge profile:

TEST 2: Cell 5 having a different temperature

Cell 01-04 and cell 05 starts 310 K and cell 05 starts from 299.1 K with higher oscillation as compared to other cells because of faulty design. At the end of the simulation cell 04 and cells 10 have a final temperature close to 315 K and cell 5 achieving temp of 328K

SOC:

Conduction;

CEll 04-05

Heat transfer coefficient: -21.28 W/(m^2K)

Thermal Conductivity: -10.64W/mK

Heat transfer coefficient: 20.12W/(m^2K)

Thermal Conductivity: 10.06W/mK

Heat transfer coefficient:-71.3W/(m^2K)

Thermal Conductivity: -15.55W/mK

Cell 05

Heat transfer coefficient: -13.4W/(m^2K)

Thermal Conductivity: -26.19W/mK

Cell 06-10

Heat transfer coefficient: -70.86W/(m^2K)

Thermal Conductivity: -15.51W/mK

Discharge profile

TEST 3

Cells having temperature in ascending order.

From the above graph, we can observe that cell 10 temperature drops from 330 K to 315 K and cell 04 temperature rise from 310 K to 315 K. cell 05 with faults has a temperature rise from 320 K to 330 K.

Conduction:

Convection:

Cell 05

Cell 06 - 10

Cyclic charge-discharge cycle

Test 4

Cells having temperatures in descending order.

Cell 04 has a temperature drop from 350 K to 315 K. We can also observe that cell 05 has a temperature rise above 330 K . Cell 10 has a temperature rise from 300 K

SOC