Project 5

In this project we make a battery model which can allow to simulate Battery charge/discharge characteristics along with aging and temperature effect of 10 series connected cell. For this purpose we use Generic battery model in simulink environment and simulate aging and temperature effect. take a look at this model first.

Here we connect 10 series Battery having 7.2V nominal voltage and 5.4Ah capacity, this is the inbuit data of the battery pack that will open when you first introduce the block, and we're not changing the model except for Battery response time(2) and Aging model sampling time(10s) but we adjust all other parameters of our model to observe aging efffect of battery in different ambient temperature, Charging/Discharging rate. The parameters of Battery pack is given below,

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. So we take a Bus selector to select the signals from the 'm' port of the generic battery and I give Ambient temperature by a constant block and I also measure The voltage and current of the battery pack by voltage and current measurement block. and I use a controlled current source to take charge and discharge current from the battery pack.

The input to the controlled current source is given by the charge/discharge logic implemented in matlab chart where I create a charging and discharging state which changes with the SOC value.

Here we can see the chart intialise with Discharging state and entry value of current I=2.3478 Amp as discribed in the aging model and the state changes when SOC=0 (Battery fully discharged) and enter the Charging state with current I=-2.3478(negative for charging) and it will again changes state when SOC will become 100%(fully charged case), and this will be continue for the whole simulation time.

Now we simulate the model for 20 hour with 25oC25oC and check the results that are shown below....

The above figure shows the total voltage and current of the battery pack. the voltage is 10 times of the cell voltage and current is same as the cell current due to series connection and we can see here the cell starts discharging first then achieve its lowerr cutoff voltage and start charging and it charges to the maximum voltages and starts discharging again.

Here we can see for charging and discharging rate same as 2.3478 Amps the battery complete 4 charge and discharge cycle in 20 hours and we can see the Voltage varying with the SOC value and cell temperature is rise to around 36oC36oC and stays in that with some rippleand we can see the age of the cell is exactly rises to 1 after one complete life cycle of the battery because we take the rated value of charging and discharging current with the temperature value which is described in the model. The maximum capacity of the battery pack is reducing exactly according to the Age equalent life cycles.

Temperature Case:- Now we just take all the same value of all other parameter but we change the ambient temperature to 45oC45oC and now take a look at the results once again.

Here we can see the charge and Dischrge characteristics are same as previous by cell temperature rises to around 57oC57oC and age of the cell is increased to around 1.6(grater than 1) for the 1 life cycle, and Battery capacity is also reduce more compare to previous case.

Even though the charging and discharging rates are same the cell temperature will affect the age of the battery and battery can derate at faster rate.

Discharge rate Case:- Now take the temperature as25oC25oC but this time we increase the Discharge current to 10A by keeping all other parameter same now observe the graphs....

here we can see the charging current is same as previous and discharging current is 10A so the Battery discharges in less time while charging of battery pack takes longer time but in meanwhile the cell completed almost 7 life cycles and also ripple in temperature increases due to high discharging current and low charging current(cell will have time to cool down). overall the temperature will have average value around 50oC50oC and age of the battery increases around 1.5/cycle and capacity of battery will reduce to same ratio. so Higher Discharge current will have derating effect of battery even all other parameters are same. The discharge current will also effect the cell temperature hence the aging.

Charging rate Case:- Now we take all other parameters as first case except for charging current, that we changed to 3 Amps.

here we can see the discharging current is same as previous and charging current is 5A so the Battery charges in less time while discharging of battery pack takes longer time but in meanwhile the cell completed almost 6 life cycles in 20 hous and also ripple in temperature increases due to high charging current and low discharging current(cell will have time to cool down). overall the temperature will have average value around 42oC42oC and age of the battery increases around 1.25/cycle and capacity of battery will reduce to same ratio. so Higher charging rate will have derating effect of battery even all other parameters are same. The charge current will also effect the cell temperature hence the aging.

Thermal Effect on Battery:- As we know the Ambient temperature will effect the Battery performance so now we try to analyse how an Lower Ambient Temperature will reduce the battery performance. To simulate this effect we take same procedure that we follow in this project and take the same value as first case as charging current=discharging current=2.3478A. But I change the Ambient temperature to −10oC-10oC and I run the model to get the simulation results....

Here we can see the model will run for is greater than 4.5 life cycle in 20 hour, which is higher than the first case because the cell capacity is reduced due to lower cell temperature which is around zero degree celsius. and we can see the maximum capacity is iinstantly reduced to less than 5.25Ah and also the Aging effect reduced to almost 0.4/cycle so we can say that the Aging effect will reduced with the cell temperature and it also reduce the maximum capacity of the battery for that time(as we increase the cell temperature the capacity will recover according to the Age of the battery.

Conclusion:-

We can conclude that the Age of the Battery pack will effect by Temperature, Charging rate and Discharging rate. Lower value of the temperature, charging rate, discharging rate will results in reduced aging effect of battery pack and Higher life cycle can achieved. but the temperature of the Battery pack can effect the capacity of the battery independently, but its not permanent as the capacity of the battery recovered with the increase in temperature, although aging of the battery is irreversible.