Project 2 Thermal modeling of battery pack

Thermal modelling of battery pack

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 model 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.

Thermal Reference

Reference connection for thermal ports Thermal Elements

Library:

Description

The Thermal Reference block represents a thermal reference point, that is, a point with an absolute zero temperature, concerning which all the temperatures in the system are determined.

Controlled Heat Flow Rate Source

Variable source of thermal energy, characterized by heat flow expand all in page

Library:

Description

The Controlled Heat Flow Rate Source block represents an ideal source of thermal energy that is powerful enough to maintain specified heat flow at its outlet regardless of the temperature difference across the source.

Connections A and B are thermal conserving ports corresponding to the source inlet and outlet, respectively. Port S is a physical signal port, through which the control signal that drives the source is applied. You can use the entire variety of Simulink signal sources to generate the desired heat flow variation profile. The heat flow through the source is directly proportional to the signal at the control port S.

The block positive direction is from port A to port B. This means that a positive signal at port S generates heat flow in the direction from A to B.

Thermal Mass

Mass in thermal systems

Library

Description

The Thermal Mass block represents a thermal mass, which reflects the ability of a material or a combination of materials to store internal energy. The property is characterized by the mass of the material and its specific heat. The thermal mass is described with the following equation: Q=c·m*dT/dt

Temperature Sensor

Ideal temperature sensor

Library

Description

The Temperature Sensor block represents an ideal temperature sensor, a device that determines the temperature differential measured between two points without drawing any heat.

Connections A and B are thermal conserving ports that connect to the two points where the temperature is being monitored. Port T is a physical signal port that outputs the temperature differential value.

The block positive direction is from port A to port B. The measured temperature is determined as T = TA  – TB.

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

For cell 01 to 04

 

Number of connected in series are:-4

Initial temperature:-299.1 k

For cell 5 cells (fault setup) in this cell, I have done changes in the electrical systems of the cell so that we can see the fault.

Number of connected in series are=4

Initial temperature=299.1 k

Capacity(A*hr)=Capcity_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 connected in series are:-5

Initial temperature:-299.1 k

PARAMETERS:

Battery configuration:

Temperature Source

A constant source of thermal energy, characterized by temperature

Library:

Description

The Temperature Source block represents an ideal source of thermal energy that is powerful enough to maintain a specified temperature at its outlet regardless of the heat flow consumed by the system.

The source generates constant absolute temperature, defined by the Temperature parameter value. here I used ambient block and set the temperature for 299.1k or 25.95 C

THERMAL ELEMENTS

Conductive Heat Transfer Heat transfer by conduction

Library

Description

The Conductive Heat Transfer block represents a heat transfer by conduction between two layers of the same material. The transfer is governed by the Fourier law and is described with the following equation: Q=k·AD(TA−TB)

Where;

Q          Heat flow

K           Material thermal conductivity

A           Area normal to the heat flow direction

D           Distance between layers (thickness of material)

TA,TB   Temperatures of the layers

Connections A and B are thermal conserving ports associated with material layers. The block positive direction is from port A to port B. This means that the heat flow is positive if it flows from A to B.

The is done from the 2 sets of blocks .one is for cell 04 to 05 and another is used for 05 to 06.

Convective Heat Transfer

Heat transfer by convection Library

Library

Description

The Convective Heat Transfer block represents a heat transfer by convection between two bodies using fluid motion. The transfer is governed by the Newton law of cooling and is described with the following equation:

Q=k·A·(T_A−T_B)

Q         Heat flow

k          Convection heat transfer coefficient

A          Surface area

T_A,T_B   Temperatures of the bodies

Connections A and B are thermal conserving ports associated with the points between which the heat transfer by convection takes place. The block positive direction is from port A to port B. This means that the heat flow is positive if it flows from A to B.

Temperature Sensor

Ideal temperature sensor

Library

Description

The Temperature Sensor block represents an ideal temperature sensor, a device that determines the temperature differential measured between two points without drawing any heat.

Connections A and B are thermal conserving ports that connect to the two points where the temperature is being monitored. Port T is a physical signal port that outputs the temperature differential value.

The block positive direction is from port A to port B. The measured temperature is determined as T = TA  – TB.

Electrical Elements:-

here the output of one cell is connected with the SOC calculation whereas the output is connected to with AC source for the cyclic charge/discharge profile

AC Current Source

The ideal sinusoidal current source

Library

Description

The AC Current Source block represents an ideal current source that maintains the sinusoidal current through it, independent of the voltage across its terminals. The output current is defined by the following equation: I=I0⋅sin(2π⋅f⋅t+φ)

The peak amplitude is set to 50 A for a cyclic charge and discharge. A basic parameter of AC source is as,

The ideal AC source maintains the sinusoidal current through it, independent of the voltage across its terminals. The output current is defined by I=I0*sin(2*pi*f*t+PHI) I0 is the peak amplitude,f is the frequency in Hz, and PHI is the phase shift in radians.

Current Sensor

The current sensor in electrical systems

Library

Description

The Current Sensor block represents an ideal current sensor, a device that converts current measured in any electrical branch into a physical signal proportional to the current.

Connections + and – are electrical conserving ports through which the sensor is inserted into the circuit. The connection I am a physical signal port that outputs the measurement result.

Electrical Reference

Connection to electrical ground

Library

Description

The Electrical Reference block represents an electrical ground. Electrical conserving ports of all the blocks that are directly connected to the ground must be connected to an Electrical Reference block. A model with electrical elements must contain at least one Electrical Reference block.

Soc Calculation:

For SOC calculation here I used gain block. integrator and sum block sum with PS Simulink converter.

For the study, we have some observation where we getting results for different cell temperature here we have set ambient temperature is to 299.1 k or 25 c

Battery Pack Configuration:

Test	Ambient temperature (k)	Cell temperature (k) (01-04)	Cell temperature (k) (5)	Cell temperature (k) (06-10)	Observation
Test – 1	299.1	299.1	299.1	299.1	Equal temp.
Test – 2		310	299.1	310	Cell 5 min. temp.
Test – 3		310	320	320	Low to high temp.
Test – 4		350	325	30	High to low temp.
Test – 5		310	350	310	Cell 5 max. temp.

RESULTS:

To check the conduction, convection, and charge and discharge rate plot we used the simscape results option.

• TEST - 1 

1. Cell temperature:

2. SOC:

3. Conduction:

Conduction is basically heat flow rate(Q) and temperaturedifference wrt time.

For cell 04-05

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

Thermal conductivity -10.66 W/m K

For cell 05 - 06

The heat transfer coefficient is 20.12 W/(m2K)

Thermal conductivity 10.06 W/m K

4. Convection:

Convection is the process of heat transfer by the bulk movement of molecules within fluids such as gases and liquids

For cell 01-04

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

Thermal conductivity -15.76 W/m K

For cell 05

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

Thermal conductivity -26.92 W/m K

For cell 06-10

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

Thermal conductivity -16.36 W/m K

5. Charge and Discharge profiles:

I(current)=1.4695e-13 A

v(voltage)= 36.334 volt

• TEST – 2

1. Cell temperature:

2.SOC:

3.Conduction:

For cell 04-05

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

Thermal conductivity -10.66 W/m K

For cell 05-06

The heat transfer coefficient is 20.12 W/(m2K)

Thermal conductivity 10.06 W/m K

4. Convection:

For cell 01-04

The heat transfer coefficient is -71.63 W/(m³K) Thermal conductivity -15.62 W/m K

For cell 05

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

Thermal conductivity -26.28 W/m K

For cell 06-10

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

Thermal conductivity -16.36 W/m K

5. Charge and Discharge

I(current)= 1.4695e-13 A

v(volt)=36.33 v

• TEST – 3

1. Cell Temperature:

2. SOC:

Conduction:

For cell 04-05

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

 Thermal conductivity -10.66 W/m K

For cell 05-06

The heat transfer coefficient is 20.97 W/(m2K)

Thermal conductivity 10.06 W/m K

4. Convection:

For cell 01-04

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

Thermal conductivity -15.75 W/m K

For cell 05

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

Thermal conductivity -26.28 W/m K

For cell 06-10

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

Thermal conductivity -16.34 W/m K

5. Charge and Discharge profile:

I(current)= 1.4695e-13 A

v(volt)=36.33 v

• TEST – 4

1. Cell Temperature

2. SOC:

3. Conduction:

 For cell 04-05

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

Thermal conductivity -10.66 W/m K

For cell 05-06

The heat transfer coefficient is 20.84 W/(m2K)

Thermal conductivity 10.06 W/m K

4. Convection:

For cell 01-04

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

Thermal conductivity -15.62 W/m K

For cell 05

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

Thermal conductivity -26.28 W/m K

For cell 06-10

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

Thermal conductivity -16.22 W/m K

5. Charge and Discharge profiles

I(current)= 1.4695e-13 A

v(volt)=36.33 v

• TEST – 5

1.Cell Temperature:

2.SOC:

3.Conduction:

 For cell 04-05

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

Thermal conductivity -10.66 W/m K

For cell 05-06

The heat transfer coefficient is 20.12 W/(m2K)

Thermal conductivity 10.06 W/m K

4. Convection:

For cell 01-04

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

Thermal conductivity -15.62 W/m K

For cell 05

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

Thermal conductivity -26.28 W/m K

For cell 06-10

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

Thermal conductivity -16.22 W/m K

5. Charge and Discharge profile:

I(current)= 1.4695e-13 A

v(volt)=36.33 v

CONCLUSIONS:

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

There are slight changes in cyclic charge and discharge as I fixed peak amplitude at 50 A.

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

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

REFERENCE:

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