Project 2 Thermal modeling of battery pack

Project 2 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 sources in different hybrid and electric vehicle, however, the operation 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 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 itself. 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 with Fault is 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 modelled 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 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.

A Detail design of MATLAB Simulink for thermal Modelling is given as

Cell 01 to 04 Subsystem

Cell subsystem basically consist of a Thermal Model and Lithium Cell 1RC block which calculate the temperature and thermal effect for cells and overall calculate for the battery pack.

The block which are inside the cell subsystem are PS Gain block which multiplies the input physical signal by a constant i.e. y = u." gain. Another block are voltage sensor and current voltage source.

The voltage sensor block represents an ideal voltage sensor, that is, a device that converts voltage measured between any electrical connections into a physical signal proportional to the voltage.

Current voltage source represents an ideal voltage source that is powerful enough to maintain the specified voltage at its output regardless of the current passing through it. The output voltage is V-Vs, where Vs is the numerical value presented at the physical signal port.

Thermal Model Subsystem

The important block which is inside the thermal model subsystem are:

• Thermal Reference: This block represents a reference point in a thermal network where the temperature is equal to absolute zero.
• Controlled heat flow rate source: This block represents an ideal energy source in a thermal network that can maintain a controlled heat flow rate regardless of the temperature difference. The heat flow rate is set by the physical signal port S. A positive heat flow rate flows from port A to port B.
• Thermal Mass: This block models internal energy storage in a thermal network. The rate of temperature increase is proportional to the heat flow rate into the material and inversely proportional to the mass and specific heat of the material.
• Temperature Sensor: This block measures temperature in a 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 the temperature at port A is greater than the temperature at port B.

Lithium Cell 1RC Subsystem

This block basically consists of capacitance value © table which depends on an external physical signal inputs SOC and T. It is assumed that the capacitance value is slowly varying with time, and hence the equation i = C'dv/dt holds.

Resistance value (R) table which depends on an external physical signal inputs SOC and T.

Voltage value (EM) which implements the cell's main branch voltage source, and determines values for capacity (C) and state of charge (SOC). The defining equations depend on cell temperature, T.

Thermal Behaviour and Fault setup

Lithium lon cell one RC-Branch equivalent circuit detail for 10 cells.

For cell 01 to 04

• Number of series-connected cells are 4
• Initial Temperature is 299.1 K

cell 05 (fault setup) In this cell I have done some changes in Electrical system of cell so that we can see the fault.

• Number of series-connected cells are 1
• Initial Temperature is 299.1 K
• Capacity (Athr) - Capacity_LUT *0.95
• Em open-circuit voltage (volts) Em_LUT*0.9
• RO terminal resistance (ohms) = RO_LUT*5
• R1 cell resistance (ohms) R1_LUT*5
• C1 capacitance (farads) = C1_LUT*0.95

For cell 06 to 10

• Number of series-connected cells are 5
• Initial Temperature is 299.1 K

Screenshot of dialogue box with detail changes.

Here the output of one cell is connected with the SOC calculation whereas other output is connected with AC current source for cyclic charge/discharge profile.

The peak amplitudes set to 50 A for cyclic charge and discharge. A basic parameter of AC current source is as

The ideal AC current source maintains the sinusoidal current through it, independent of the voltage across its terminals. The output current is defined by 1-10* sin(2"pi'f't- PHI), where 10 is the peak amplitude, f is the frequency in Hz, and PHI is the phase shift in radians.

The other block which are used in lithium ion battery pack are as:

• Temperature Source: This block represents an ideal energy source in a thermal network that can maintain a constant absolute temperature at the port regardless of the heat flow rate.

Here I used this block for ambient temperature and which I set as 299.1 K or 25.95 C.

• Convective Heat Transfer: This 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, and surface area in contact with the fluid.

Here I use 3 blocks for convection.

• Conductive Heat Transfer: This block models heat transfer in a thermal network by conduction through a layer of material. The rate of heat transfer is governed by Fourier's law and is proportional to the temperature difference, material thermal conductivity, area normal to the heat flow direction, and inversely proportional to the layer thickness.

The conduction is done from the 2 set of blocks, 1 block used for 01-04 and other is used for cell 06-10.

for cell 06-10

-for cell no 06 to 10 the falling from zero to the negative zone the oscillation are less. at the end of the simulation

The heat transfer coefficient is -82.63 W/(m²K)

Thermal conductivity -16.36 W/m K

e) Charge & Discharge Profiles :-

-in the charge and discharge rate graph the voltage and current oscillating from pretty highly where current is ranging from -50 t0 50 A and voltage is ranging from 30 to 43 volts

the final value at the end of the simulation for

I(current)=1.4695e-13 A

v(voltage)= 36.334 volt

Test Case 2 :-

a) Cell Temp.

here the cell no 04 and cell no 10 starting from a temp of 310 k at the start of simulation and cell no 5 from 299.1k with higher oscillation as compared to the other cells because of faulty design.at the end of the simulation the cells 04 and 10 having the final temp of nearby 315k and cell no 5 achieving the temp of 328k.

b) SOC

C) Conduction

for 04-05

the heat flow rate plot starts from 20 and falls into the negative zone and the temperature difference plot starts from 10 and falls into the negative zone and oscillate at the end of the simulation the final value for

The heat transfer coefficient is -21.32 W/(m²K)

Thermal conductivity -10.66 W/m K

for cell 05-06

-for cell, no 05-06 the plot initiate from the negative zone and at the end settle down in the positive zone where the final values for,

The heat transfer coefficient is 20.12 W/(m²K)

Thermal conductivity 10.06 W/m K

d) Convection

for cell 01-04

-for cell, no 01-04 the plots remain in the negative zone throughout the simulation with pretty low oscillation with falling nature and the final values at the end of the simulation are,

The heat transfer coefficient is -71.63 W/(m²K)

Thermal conductivity -15.62 W/m K

for cell 05

-for cell no 5 the initial values are O and falling into the negative side with high oscillation because of the fault and the final values are

The heat transfer coefficient is -13.66 W/(m²K)

Thermal conductivity -26.28 W/m K

for cell 06-10

For cell, no 06-10 the plot remains on the negative side, and falling at the end of the simulation the final values are.

The heat transfer coefficient is -82.64 W/(m²K)

Thermal conductivity -16.36 W/m K

e) Charge & Discharge

-charge and discharge rate profile the plot for current is ranging in between -50 to 50 A and the voltage 30 to 43 volt and the final values for

I(current)= 1.4695e-13 A

v(volt)=36.33 v

Test Case 3 :-

a) Cell Temp.:-

-the initial temperature for cell no 04 is 310K, cell no 5 is 320 K and cell no 10 is 330K, but after some point, cell no 04 and cell no10 started following the same temperate rate, and cell no 5 starts oscillating with high value because of fault, the final value for cell no 04 and 10 is around 316K and fro cell no 5 is 328K because of its fault design

b) SOC :-

C) Conduction :-

For Cell 04-05

-for cell 04-05 the plot starts from the negative side and drops and then again increases and maintains throughout the simulation negative zone, the final values at the end of the simulation are

The heat transfer coefficient is -21.32 W/(m²K)

Thermal conductivity -10.66 W/m K

for cell 05-06

-for cell, no 05-06 both the plot starts from the negative side and then entered into the positive side and the final value at the end of the simulation are

The heat transfer coefficient is 20.97 W/(m²K)

Thermal conductivity 10.06 W/m K

d) Convection:-

for cell 01-04

-for cell no 01-04 the final values at the end of the simulation are

The heat transfer coefficient is -71.64 W/(m²K)

Thermal conductivity -15.75 W/m K

for cell 05

-for cell no 5 the final value at the end of the simulations are

The heat transfer coefficient is -13.39 W/(m²K)

Thermal conductivity -26.28 W/m K

for cell 06-10

-for cell no 06 -10 the final values at the end of the simulation are

The heat transfer coefficient is -83.30 W/(m²K)

Thermal conductivity -16.34 W/m K

e) Charge and Discharge Profile :-

-charge and discharge rate profile the plot for current is ranging in between -50 to 50 A and the voltage 30 to 43 volt and the final values for

I(current)= 1.4695e-13 A

v(volt)=36.33 v

Test Case 4:-

a) Cell Temp.:-

-for cell no 04 the initial temperature is 350 K, cell no 10 is 305 K and for cell no 5 the temperature is 325 K. both the temperature of cell no 04 and 10 started following the same temperature rate after the time period of 2000 sec and on the other hand, the cell no 5 is designed for fault oscillates with high temperature. the end temperature of cell no 04 and 10 are near about 315 K(the cell no 4 have little less value then cell no 10 because of the no of cells involved) and for cell no 5 having a temperature at the end is 328 K

b) SOC :-

C) Conduction

for cell 04- 05

-for cell no 04-05 the final values at the end of the simulation are,

The heat transfer coefficient is -21.32 W/(m²K)

Thermal conductivity -10.66 W/m K

for cell 05 - 06

for cell no 05-06 the final values at the end of the simulation are,

The heat transfer coefficient is 20.84 W/(m²K)

Thermal conductivity 10.06 W/m K

d) Convection

for cell 01-04

-for cell no 01-04the final values at the end of the simulation are,

The heat transfer coefficient is -72.13 W/(m²K)

Thermal conductivity -15.62 W/m K

for cell 05

-for cell no 5 the final values at the end of the simulation are

The heat transfer coefficient is -13.39 W/(m²K)

Thermal conductivity -26.28 W/m K

for cell 06-10

for cell no 06-10 the final value at the end of the simulation is

The heat transfer coefficient is -83.20 W/(m²K)

Thermal conductivity -16.22 W/m K

e) charge and Discharge profiles

-charge and discharge rate profile the plot for current is ranging in between -50 to 50 A and the voltage 30 to 43 volt and the final values for

I(current)= 1.4695e-13 A

v(volt)=36.33 v

5) Test Case 5:-

a) Cell Temp.:-

-for cell no 04 and 10 having the same initial temperature of 310 k and having the same temperature rate throughout the simulation. just small difference is cell 10 having a high temperature than cell no 4 because the no of cells is different and cell no 5 which is design for fault having an initial temperature of 350K with high oscillation. Cells no 04 and 10 having the temperature value at the end of the simulation around 315 K and cell no 05 having a temperature of 325 K at the end of the simulation.

b)SOC

C) Conduction

for Cell 04-05

-for the cell 04-05 the value at the end of the simulations are

The heat transfer coefficient is -21.32 W/(m²K)

Thermal conductivity -10.66 W/m K

for cell 05-06

-For cell 05-06 the values at the end of the simulation are

The heat transfer coefficient is 20.12 W/(m²K)

Thermal conductivity 10.06 W/m K

d) Convection

for Cell 01-04

-for cell no 01-04 the values at the end of the simulations are

The heat transfer coefficient is -71.64 W/(m²K)

Thermal conductivity -15.62 W/m K

for cell 05

-for cell no 5 the values at the end of the simulation are,

The heat transfer coefficient is -13.68 W/(m²K)

Thermal conductivity -26.28 W/m K

for Cell 06-10

-for cell 06-10 the values at the end of the simulation are,

The heat transfer coefficient is -83.32 W/(m²K)

Thermal conductivity -16.22 W/m K

e) Charge & Discharge

charge and discharge rate profile the plot for current is ranging in between -50 to 50 A and the voltage 30 to 43 volt and the final values for

I(current)= 1.4695e-13 A

v(volt)=36.33 v

CONCLUSIONS:

1)As the difference in temperature we can observe the changes in heat flow rate by conduction and convection.

2) The re are slight changes in cyclic charge and discharge as I fixed peakamplitude at 50 A

3)SOC for all the temperature remain the same so there is no difference in SOC graphs

4) cell no 5 had higher oscillation and we can observe that in every graph because we design that cell for fault