Project 5

Aim : To make a Battery model of 10 series connected cells to simulate the aging and thermal effects at different charge and discharge rates.

Objective :

• Calculate voltage & Current of battery pack
• To calculate SoC of battery

Introduction :

SoC -

1. The state of charge (SOC) is a measurement of the amount of energy available in a battery at a specific point in time expressed as a percentage.
2. If the initial charge in the battery is known, from then on "Coulomb Counting" can be used to calculate its SOC.
3. In the project we are using coulomb counting method to calculate SOC

Coulomb Counting Method -

1. The Coulomb counting method is associated with monitoring the input and the output current continuously. Since capacity is the integral of current with respect to time, by measuring the input and the output current, change in capacity or capacity degradation of a battery can be measured easily.
2. The coulomb counting method, also known as ampere hour counting and current integration, is the most common technique for calculating the SOC. This method employs battery current readings mathematically integrated over the usage period to calculate SOC values given by
   
3. where SOC(t0) is the initial SOC, Crated is the ratedcapacity, Ib is the battery current, and Iloss is the current consumed by the loss reactions. The coulomb counting method then calculates the remaining capacity simply by accumulating the charge transferred in or out of the battery.
4. 

Simulink Model -

• The model consist of two subsytems for 10 cells of series connected battery pack and another for coulomb counting method.
• 10 Li-ion cells are connected in series to form a battery pack.Each cell having 7.2 nominal voltage and 5.4 rated capacity.
• 10 series Battery model is identical and together they make 7.2*10 = 72V Battery pack model with 5.4Ah capacity. As the battery model is identical we only observe parameters of first battery and assume It will be same for all other cells.
• The output from the battery pack it taken from the m potr of cell through a bus selector to observed all the parameters of the pack on the the scope.
• Ambient tempreture block is used as reference temp to battery which is 25
• Current anf Voltage measurment blocks are connected across the batter pack to check the current and voltage.
• Cells connection and parameter setting are given below -

• The coulomb counting block is made up from integrator & gain block. the gain block is connected to the current measument output signal.
• We are build this model for 1 C- rate. As our max. voltage and rated capacity is same so battery can be discharge by c-rate of 1 it means it take 1 hour to fully discharge so,SoC is zero after one hour.
• The coulomb counting method is used for SOC calculation but it is not providing accurate values so because of that we are connected a display to SOC signal of bus selector to observe actual values.
• After running the model for 10 sec we can observed the result on the scope and display.

Results :

Current, Voltage, Tempreture and SoC level is shown in the below plots for thr time frame of 10 sec.

Conclusion :

• We are implemented this model for C - rate of 1 , it takes 1 hour to discharge the battery and in 30 min means 1800 sec the SoC is 50%
• Lower value of the temperature, charging rate, discharging rate will results in reduced aging effect of battery pack and Higher life cycle can achieved.