Project 2 Thermal modeling of battery pack

Q : 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.

A : INTRODUCTION:

The temperature of a Lithium battery cell s important for its performance, efficiency, safety, and capacity and is influenced by the environmental tem perature and by the charging and discharging process itself. Battery Management Systems (BMS) take into account this effect As the temperature at the battery cell is difficult to measure, often the temperature is measured on or nearby the poles of the cell. although the accuracy of predicting the cell temperature with those quantities is limited. Therefore a thermal model of the battery is used in order to calculate and estimate the cell temperature.

This project uses a simple representation for the thermal model and shows how the thermal parameters are identified using input/output measurements only, where the load current of the battery represents the input while the temperatures at the poles represent the outputs of the measurement. Witha single measurement, the eight model parameters (thermal resistances, electric contact resistances, and heat
capacities) can be determined using the method of least-square. Experimental results show that the simple model with the identified parameters fits very accurately to the measurements.

OBJECTIVES :

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.

STUDY:

For a 10 cell series lithium-ion battery model,. simulating the thermal effects and comparing life cycle performance at various temperatures charge & discharge rates using MATLAB:

So, for the 10-cell series lithium-ion battery pack, We used MATLAB Simulink for finding a thermal effect and life cycle performance related to temperature, charge, and discharge.

A Default Matlab Simulink Model of Lithium-lon Battery Pack With Fault which We used for 10-cell Battery Pack Thermal Modelling-

• Lithium-lon 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 celltemperatures
• 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 is 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.

Matlab Simulink Model of 10-cell Series Lithium-lon Battery Pack for Thermal Modelling-

Battery Pack Model Explanation :

Cell 01 to 04 Subsystem Block -

• Cell subsystem basically consists of a Thermal Model and Lithium Cell 1RC block which calculates the temperature and thermal effect of the battery pack.
• The block which are inside the cell subsystem is PS Gain block which multiplies the input physical signal by a constant i.e. y = u gain. Other blocks are the voltage sensor and Controlled-voltage source.
• The voltage sensor block represents an ideal voltage sensor, that's converts voltage measured between any electrical connections into a physical signal proportional to the voltage.
• A controlled voltage source represents an ideal voltage source that is powerful enough to maintain the specified voltage at ts 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 Block -

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 model 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 Block-

• 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 equationi = 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.

Block Parameters For Cells :

For Cell 01 to 04 -

The value of intial Cell temparature (T_init) is the same for all cells, Which is 293.15 K.

For Cell 05 (fault setup)-

In this cell, We have done some changes in the Electrical system of the cell so that we can see the fault.

For Cell 06 to10 -

AC Cuurent Source Block with Parameters -

The peak amplitude was set to 50A for cyclic charge and discharge.

The Other Blocks which are used in the lithium-ion battery pack are as Following :

Temparature Source -

Here we used this Block for ambient temparature and ambient temparature(T_init) is set as 293.15 K or 20degrees C.

Convective Heat Transfer -

• This block modelsheat transfer in a thermal network by convection due to fluid motion. The rate of heat transfer is proportional to the temparature difference, heat transfer coefficient, and surface area in contact with the fluid.
• Here we use 3 blocks for convection for 3 different cell packs.

Conductive Heat Transfer -

The conduction is done from the 2sets of blocks, 1 block is used for 04-05 and the other is used for cells 05-06.

SOC Estimation Model -

• For SOC calculation here we used Gain block, Integrator, and Sum block with PS Simulink convertor.
• This model estimates the battery SOC % using the coulomb counting method. The initial SOC of the battery is assumed to be 100%(1).
• The Coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC.
• This subsystem takes current as input and gives the battery SOC % as output. A current sensor block is used to measure discharge current and connected to soc estimation.

Qutput Scope Results:

Simulation-Based on Different Cell Temperature -

In this simulation, We set ambient temperature 293.15 Kor 20 °C and another cell temperature are as follow-

Test Ambient Temparature (K) Cell Temparature(K)(01-04) Cell Temparature(K)(05) Cell Temparature(K)(06-10)

Test 1 293.15 293.15 293.15 293.15

Test 2 293.15 299.15 293.15 299.15

Test 3 293.15 310.15 320.15 310.15

Test 4 293.15 320.15 320.15 320.15

Colour Indication for Cells -

Yellow colour - Cell 4

Purple colour - Cell 5 (Fault)

Green colour - Cell 10

Test -1

Ambient Temparature (K) Cell Temparature(K)(01-04) Cell Temparature(K)(05) Cell Temparature(K)(06-10)

293.15 293.15 293.15 293.15

Cell Temparature Plot -

As we can see that there is much fluctuation in cell 05 due to fault.

SOC PLot -

As we see that the battery is fluctuating every 301.200 seconds which depend upon the thermal behaviour of the battery pack.

Conduction :

Conduction is basically here Heat Flow rate (Q) and Temparature Difference(T) Vs Time.

Convection -

The above graph Highlights the heat flow rate and temparature difference by convection Medium.

Cyclic Charge/ Discharge Profile -

Charge and discharge profiles are depending upon Current(I) and Voltage(V) vs Time. The cyclic charge and discharge were calculated at 50A peak amplitude.

Test -2

Ambient Temparature (K) Cell Temparature(K)(01-04) Cell Temparature(K)(05) Cell Temparature(K)(06-10)

293.15 299.15 293.15 299.15

Cell Temparature Plot -

As we can see that in cell 5 the temparature rice to 310 k and it goes fluctuating from 317 K to 330 K and end at 334 K.

SOC Plot -

As we see that the battery is fluctuating every 301.200 seconds which depend upon the thermal behaviour of the battery pack.Conduction is basically here Heat Flo rate (Q) and Temparature Difference (T) Vs Time.

Conduction -

Conduction is basically here Heat Flo rate (Q) and Temparature Difference (T) Vs Time.

Convection -

The above graph highlights the heat flow rate and temparature difference by convection Medium.

Cyclic Charge / Discharge Profile -

Charge and discharge profiles are depending upon Current(I) and Voltage(V) vs Time. The cyclic charge and discharge were calculated at 50A peak amplitude.

Test -3

Ambient Temparature (K) Cell Temparature(K)(01-04) Cell Temparature(K)(05) Cell Temparature(K)(06-10)

293.15 310.15 320.15 310.15

Cell Temperature Plot -

As we can see that in cell 5 the temparature rice to 325 K and it goes fluctuating from 327 K to 331 K and end at 334 K.

SOC Plot -

As we see that the battary is fluctuating every 301.200 seconds which depend upon the thermal behaviour of the battery pack.

Conduction -

Conduction is basically here Heat Flow rate (Q) and Temparature Difference (T) Vs Time.

Convection -

The above graph highlights the heat flow rate and temparature difference by convection Medium.

Cyclic Charge /Discharge Profile -

Charge and discharge profiles are depending upon Current (I) and Voltage (V) vs Time. The cyclic charge and discharge were calculated at 50A peak amplitude.

Test - 4:

Ambient Temparature (K) Cell Temparature(K)(01-04) Cell Temparature(K)(05) Cell Temparature(K)(06-10)

293.15 320.15 320.15 320.15

Cell Temparature Plot -

As we can see that in cell 5 the temparature rice to 330 K and it goes fluctuating from 333 k and 331 K end at 334 K.

SOC Plot -

As we see that the battery is fluctuating every 310.200 seconds which depend upon the thermal behaviour of the battery pack.

Conduction -

Conduction is basically here Heat Flow rate (Q) and Temparature Difference (T) Vs Time.

Convection -

The above graph highlights the heat flow rate and temparature difference by convection Medium.

Cyclic Charge / Discharge Profile -

Charge and discharge profiles are depending upon Current(I) and Voltage (V) vs Time. The cyclic charge and discharge were calculated at 50A peak amplitude.

CONCLUSION :

For a 10 cell series lithium-ion battery model, simulated the thermal effects and compared life cycle performance at various temparatures, charge & discharge rates using MATLAB.