Challenge

Project 2 Thermal modeling of battery pack

SSrinivas Sapati23 Aug 2021

Objective:

To design the simulink model of 10 cells series connected lithium ion battery with teperature effect and compare the life cycle at various teperature,charge and discharge.

to model the battery we have different concepts present in our simulation using thermal model of the lithium-ion battery.

Thermal model of Lithium-ion Battery:

Here we took table based battery,the block represents giving a result very similar to the original battery model,The block calculates open circuit voltage as a function of charge level and optional temperature using lookup tables and includes several modeling options.

Self-discharge
Battery fade
Charge dynamics
Calendar aging

The cell temperature can be computed by using heat equation of homogeneous body exchange heate with environment.

here

Ct -heat capacitance

T -inner cell temperature

Rt-convection resistsnace

Ps-power dissipated inside the cell

Cell state of charge and capacity:

The cell capacity will depends in the below factors

1)average cell discharge current and discharge time

2) Inner cell Temperature

3) value of the ened of charge voltage

4) storage time

5) number of charge and discharge cycles

let for short periode of time T, average cell discharge current I ,the state of charge of the cell equation is

Cq=Cq(R,T).

let the cell is fully charged at time t=0,the extracted charge from the cell is

Q(t)= intigration of current from 0 to T

where Cq is the capacity of the cell at considerd discharge current ,temperature of the cell.

soc of the cell is SOC =1- Q(t)/Cq

Euivalent circuit model parameters:

The elements which are in above quivalent circuit are functioin of temeperature and state of charge (SOC).

Ro=Ro(SOC,T)

R1=R1(SOC,T)

C1=C1(SOC ,T)

Em=Em(SOC,T)

Above parameter will estimate at different temperatures and store the values in the two dimentional look up table.

Electrical Equivalent circuit of Battery: Electrical analogy we will consider here.voltage source,capacitors,resitors elements

represents the battery behaviour.Ro represents the terminal resistance and R1,C1 combination circuit represents the dynamics of the battery.

Simulink Model:

here i selected alm12v7 lithium ion cell. 10-cells are conneted in serie with each other,total voltage of the battery pack is 32 V. in the simulink model we can see the how the temperature effects the battery life cycle ,charge and discharge currents .for charge and discharge i took the suare wave pulse with differnet currents and the frequency of the square wave is 2/3600 Hz.