Project 2 Thermal modeling of battery pack

EV BATCH17

AIM:

To design a 10 series lithium ion battery model,simulate the thermal effects by using the matlab.

abstract:

• Lithium ion (Li-ion) battery pack is a complex system consisting of numerous cells connected in parallel and series. The performance of the pack is highly dependent on the health of each individual in-pack cell. An overcharged or discharged cell connected in a parallel string could change the total capacity of the battery pack. In a pack, current-split estimation plays an important role to monitor the cell functions. Therefore, a scheme is required to estimate current-split accurately, which can thereby help to improve the overall pack performance. An overcharge model of lithium ion battery pack was built by coupling the electrochemical model with thermal abuse model. The influences of current, convection coefficient and gap between batteries on the thermal runaway propagation were studied. The results of temperature and voltage obtained from the models were validated experimentally, and they were agreed well with the experimental data with the relative error within 6%. The results showed that the onset temperature of thermal runaway of the charged battery increased with an increase in the current, while the temperatures for the other two decreased. The temperature rate of the charged battery changed little when the convection coefficient was greater than 40 W/m² K. The clamp of lithium ion battery pack had an important effect on the thermal runaway propagation. The occurrence of thermal runaway propagation was depended on whether there was the existence of clamp when the battery gap exceeded 5 mm.

INTRODUCTION:

 The lithium ion batteries are widely used as energy sources in different hybrid and electrical vehicle.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 ion battery cell is important for its performance,efficiency,safety,and capacity and is influenced by the environmental temperature and by charging and discharging process itself.Therefore,a thermal model of the battery is used in order to calculate and estimate the cell temperature.

according to performance of lithium ion battery:

The open circuit voltage is higher than in aqueous battreies (such as lead-acid,nickel-metal hydrid and nickel cadmium).Internal resistance increases with both cycling and age, although this depends strongly on the voltage and temperature the batteries are stored at. Rising internal resistance causes the voltage at the terminals to drop under load, which reduces the maximum current draw. Eventually, increasing resistance will leave the battery in a state such that it can no longer support the normal discharge currents requested of it without unacceptable voltage drop or overheating.

Lithium ion battery pack with fault was simulated.A battery pack consisting of multiple series-connected cells in a effective manner.It also shows how a fault can occurs.It can be introduced into one cells to see the impact on battery performance and cell temperatures.For efficiency,identical series-connected cells are not just simply modelled by connecting cells 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 5fault subsystem,reducing both capacity and open-circuit voltage,increasing the resistance values.

Construction of the circuit:

The detail design can be created by using the MATLAB-simulnik for the thermal modelling.

MODEL:

CELL 01 TO 04 SUBSYSTEM:

This cell 01-04 block has been created by using the library block

In simulink,you can create your own block libraries as a way to reuse the functionality of blocks or subsystems in mone or more models.if you want to reuse a set of matlab algorithm in simulink models,you can encapsulate your matlab code in a matlab function block library.

In matlab,create a new library model as a new library.

GOTO simulink Library blocks & place all the relevant blocks in library model & save it asusual.

Create  a subsystem out of it & lock the library function.Look it at in command window "set_pram(gcs,'Lock','off')".

The below figure represents the library blocks.

The subsystem can be created and it should  be masked by creating the mask by right clicking the subsytem.

The below figure shows the mask creation

inside the mask dialoge box contains the icon & ports,parameter dialog box,initialization and finally documentation.

The below figure represents all the mask parameters.

The below figure represents the parameters created for cells 01-04:

after creating the mask apply the mask.

The cell 01 to 04 subsystem basically consist of a thermal model and lithium cell 1RC block which calculate the temperature and thermal effect for cells and overall calculate the battery pack.This block which are inside the cell subsytem 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 propotional to the voltage.

The current voltage source represents an ideal voltage source that is powerful enough to maintained 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

No of connected in series are 4 

Intial temperature=299.1k 

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

 

No of connected in series =1

Intial temperature = 299.1k 

Capacity (A/hr) = 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 

 

 No of connected in series = 5 

intial temperature =299.1k 

Lithium Cell IRC Subsystem:

This block basically consists of capacitance value o 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.

Lithium cell IRC block can be created by using the create mask command,it should be created in the library page.

 The masked subsystems:

The subsystem can be masked by right click- mask-create the mask-giving the parametersand click apply.

The subsystem of C_table,R_table,C_table temperature,R_table temperature,Em_table,Em_table temperature.

C_table- contains the Models a capacitor where the capacitance value (C) 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.

R_table -Models a resistor where the resistance value (R) depends on an external physical signal inputs SOC and T.

Em_table -This block 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.

The below figure represents to create the mask.

create the parameters in the mask by clicking the edit option.

after creating the parameters,initialization command should be provide

simscape.compiler.sli.internal.preinitmask(gcb);

create the documentation of the subsytem.

after creating the mask double clicking the subsystem block,the subsystejm opens,displaying its blocks in a seperate window.

The mask dialog box and icon look like this.

done the same steps for remaing blocks like R_table,Em_table etc..

The lithium ion elements should be created by using the library page,the below figure represents the Lithium ion battery elements.

The lithium cell 1RC circuits are conncted with eachother as well as connection port.

connection port-You can manually place a Connection Port block inside a subsystem, or Simulink can automatically insert a Connection Port block when you create a subsystem within an existing network. The Connection Port block adds a port to the parent Subsystem block. The port type depends on the connection or signal it transfers.

The connected blocks of the lithium ion 1RC circuit should be showned below.

 Thermal behaviour and fault setup:

Lithium-ion 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 299.1K

For 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 299.1K

Capacity (Athr) - Capacity_LUT*0.95 .

Em open-circuit voltage (volts) = Em_LUT*0.9

RO terminal resistance (ohms) = RO_LUT 5

Rl cell resistance (ohms) = RILUT'5

Cl capacitance (farads) = CI_LUT*0,95

For cell 06 to 10 

Number of series-connected cells are 5

Initial Temperature is 299.1K

Electrical parameter per cell:

Here the output of one cell is connected with the soc calculation wheares other output is connected with AC current source for cyclic charge and discharge profile.

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

I = 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.

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

Convective Heat Transfer:

The Convective Heat Transfer block represents a heat transfer by convection between two bodies by means of fluid motion. The transfer is governed by the Newton law of cooling: Q = k ⋅ A ⋅ (T A − T B),

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.

The heat transfer coefficient is dependent on the temperature. However, Newton's law does approximate reality when the temperature changes are relatively small, and for forced air and pumped liquid cooling, where the fluid velocity does not rise with increasing temperature difference.

three convective heat transfer blocks are used the parameters of the block should be showned below.

Conductive Heat Transfer:

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:

where:

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.

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 is used for 01-04 and other is used for cell 06-10.

For SOC calculation Gain block, integrator and Sum block with PS-simulink convertor was used.

Temperature Sensor:

Ideal temperature sensor-Library - Thermal Sensors-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 th 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

 

Current Sensor :  

The current sensor in electrical systems-Library - Electrical Sensors-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

Connection to electrical ground:

Library-Electrical elements-The Electrical Reference block represents an electrical ground. Electrical conserving ports of all the blocks that are directly connec to the ground must be connected to an Electrical Reference block.. 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 299.1k or25c.

gain block:

The Gain block multiplies the input by a constant value (gain). The input and the gain can each be a scalar, vector, or matrix. You specify the value of gain in the Gain parameter.

integrator:

The Integrator block outputs the value of the integral of its input signal with respect to time

While these equations define an exact relationship in continuous time, Simulink uses numerical approximation methods to evaluate them with finite precision. Simulink can use several different numerical integration methods to compute the output of the block, each with advantages in particular applications. Use the Solver pane of the Configuration Parameters dialog box  to select the technique best suited to your application.

Subtract block:

Simulink Math Operations and Fixed-Point Blockset Math Description The Sum block performs addition or subtraction on its inputs. This block can add or subtract scalar, vector, or matrix inputs.

ps-simulink convereter:

The PS-Simulink Converter block converts a physical signal into a Simulink  output signal. Use this block to connect outputs of a Simscape physical network to Simulink scopes or other Simulink blocks. Block Icon Display on the Model Canvas.

Results:

 

Battery Pack configuration : 

To check the conduction,convection and charge and discharge rate plot

•   For Test-1 

a)Cell temperature : 

All the three the cell having the same temperature at the start which is at 2001 kbut in the beginning few seconds of simulation cell no 5 oscillates with more than the cell 4 and 10 because its design with fault and ranging to higher temp then cell 4 and 10.after a time period of around 1300 sec both the cells getting are unfollowing the temperature line which was following the same temperature rate cell no 4 and 10 having approximately 310(cell 04 having quite less temp then cell 10 because of no of the cell ore different) k at the end of the simulation and the cell no 5 achieving the higher temperature of around 324 k. 

SOC RESULT:

The SOC graph following the simulation the sinusoidal waveforms structure and fluctuating after 297 seconds and this waveform acheiving the value of more than 100.06 SOC 

Conduction : 

For cell 04-05 : 

Conduction is basically heat flow rate (Q) and temperature difference with respect to time. 

Cell no 04-05 and having a high amplitude of waveforms (for heat flow and temperature difference)which are oscillating at apretty high rate which is starting from zero and dropping in to the negative zone at the end of the simulation. 

The heat transfer coefficient is -21.32 w/(m^2k) ,Thermal conductivity -10.66 w/m k .

For cell 05-06 

 

For cell no 05-06 both the waveforms oscillating at ahigh rate but in a positve zone which are increasing intially and maintaining a certain range. 

The heat transfer coefficient is 20.12 w/(m^2k) 

Thermal conductivity 10.06 w/mk 

d)convection : convection is the process of heat transfer by the bulk of the movement of molecules within fluids such as gasses and liquids. 

For cell 01-04 : 

 

For cell no 01-04 the oscillations are pretty low and dropping in to the negative zone at the end of the simulation.the final values for  

The heat transfer coefficient is -71.63 w/(m^2k) 

Thermal conductivity -15.76 w/mk 

For cell 05 : 

 

For cell no 5 they are starting from0 and falling in to the negative zone the oscillation having high amplitude because of the faulty cell at the end of the simulation. The heat transfer coefficient is -13.39w/(m^2k),Thermal conductivity -26.92 w/mk 

• 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/(m^2k) ,Thermal conductivity -16.36 w/mk 

e) charge and Discharge profiles :

 

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

the final at the end of the simulation for I(current) = 1.4695e-13A,v(voltage) = 36.33 V  

Test-2:

1)cell temperature:

Here the cell no 04 and cell no 10 starting from a temp of 310k at the start of thesimulation and cell no 05 from 310k with higher oscillation as compared to the other cells because of the faulty design at the end of the simulation the cells 04 and 10 having the final temp of nearby 315k and cell no 5 acheiving the temperature pf 328k.

SOC:

c)Conduction : 

• For cell  04-05 : 

The heat flow rate plot starts from 20n nand falls in to the negative zone the temperature difference plot starts from 10 and falls in to the negative zone an doscillate at the end of the simulation the final valuye for  The heat transfer coefficient is -21.32w/(m^2k) ,Thermal conductivity -10.66w/mk 

For cell 05-06 :

For cell no05-06 theb plot intiate from the negative zone and at the end settle down in the positive zone where the final values for, 

d)Convection : 

For cell no 01-04 the plots remain the negative zone throughout the simulation with pretty low oscillation with falling nature and the final values at the e d of the simulation The heat transfer coefiicient is -71.63 w/(m^2k),Thermal conductivity -15.62 w/mk 

For cell 05: 

For cell no 05  the intial values are 0 and falling in to the negative side with high oscillation because of the fault and the final values are  the heat transfer coefficient is -13.66 w/(m^2k) ,Thermal conductivity -26.28 w/mk 

• for cell 06-10:

  

For cell 06-10 the plot remains on the negative side,aNnd falling at the end of the simulation the heat transfer coefficient is -82.64 w/(m^2k),Thermal conductivity is -16.36 w/mk 

e)charge and discharging: 

charge and discharge rate profilke the plot for current is ranging  in between -50 to 50A and the voltage 30 to 43 volt and the final values for  I(current) = 1.4695e-13A,v(volt) = 36.33v 

• Test 3 :

a)cell Temp : 

The intial temperature for cell no 04 is 310k,the cell no5 is 320k and cell no 10 is 330k,but after some point,cell no 04 and cell no 10 started following the same temperature rate and cell no05 starts oscillating with high values because of fault .The final value for cell no 04 and 10 is arounf 316k and cell no5 is328k 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 maintain through out the simulation of negative zone .The final values at the end of the simulation are the heat transfer coefficient is -21.32w/(m^2k) 

Thermal conductivity is -10.66 w/mk 

• For 05-06 :

For cell,no05-06 both the plot starts from the negatuive side and then enetered in to the positive side and the final value at the end of the simulation the heat transfer coefficient is 20.97w/(m^2k) ,Thermal conductivity 10.06 w/mk 

d)convection: 

cell 01 to 04:

For cell no01-04 the final values at the end of the simulation are  the heat transfer coefficient is -71.64w/(m^2k) ,Thermal conductivity -15.y75 w/mk.

For cell 06-10 :

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

The heat transfer coefficient is -83.30w/(m^2k) 

Thermal conductivity -16.34 w/mk 

1. e) Charge and discharge profile :

Charge and discharge rate profile the plot for current is ranging in between -50 to50A and the voltage 30 to43volt and the final values for  I(current) = 1.4695e-13A ,V(volt) = 36.33 .

Conclusion : 

 We can observe the temperature differences changes  the heat flow rate by conduction and convection . There are slight changes in cyclic charge and discharge as to fixed peak amplitude at 50A  SOC for all the temperature remain the same,so there is no difference in SOC groups. Cell no 5 is the fault cell because it had higher oscillation and we can observe that in every graph we design that cell for fault. The thermal effects and cycle comparison based on its performence at variuos temperature are observed.