Week 7 State of charge estimation

Question 1:

• This main block consists of two sub system BMS ECU and Plant units
• The plant output from plant unit given as input to BMS ECU as BMS input feedback loop the state request is given to BMS ECU unit
• The BMS output commands given as input to plant unit as From BMS the state request is given to plant unit
• The final outputs from closed loop model are BMS input, BMS output BMS info
• In BMS ECU unit the current power limit calculations are done used in state machine block Soc estimations cell balancing logics as shown below
• In battery pack there are two types of configurations as 1 module 6 cells and 16 modules 95 cells
• Here we are closing 1 module for lesser simulation running time
• To run three test cases from harness dashboard of closed loop BMS control:
• We have to test three cases for this model by selecting test sequence variant and select the cases one by one as follows

Test case:1

• Select from test sequence variant dialog box
• This selection consists of selection changes is marked BMS state request subsystem
• Driving for first 3000 secs
• After 3000 sec starts balancing operations occur for next 1000 secs
• Then charging and balancing occurs for next 5000 secs
• After that sequence post charge balancing operation occurs till end of the simulation
• first 3000 secs all 6 cells are drive model where discharging occur majorly and in standby mode for lesser duration at approximately 1000 to 2000 sec
• The voltage varies from 3.1 V to 3.9V in this range. From 3000sec to 4000sec cell balancing occur and this stage the module in standby mode and voltage in constant nearly 3.7V
• After 4000sec charging occur voltage raised from 3.7V to 4V at 4V to 4.2V constant voltage current reduce from 30A to 2.6A
• At end of the charging and cell balancing occurs up to 9000sec
• The temperature of cell is lesser and cell 6 has higher temperature for all stages after 4000sec temperature start increase exponentially up to constant voltage and cell balancing region up to 9000sec
• Cell 1max temperature raised up to 302k and cell 6 temperature raised upto 317k after 9000sec the temperature still reduce and remains stable at reaching ambient temperature
• initially up to 3000sec balancing as not performing after 3000sec cell balancing starts with on cell 6 and cell 2 as they raised to as shown
• After this stage charging and balancing post charge balancing are occurs as cell 6 and cell 2 remain in 1 state still end of simulation as well is in lesser voltage than

TEST case2:

• Now select test case 2 and click apply in test sequence variant dialog boxNow run the model and result can be viewed
• Dashboard result are shown
• The scope result plotted as
• Entire sequence is performing in drive mode as shown the plot. Small duration of stand by modes are not plotted in this plot a simulation 10000sec command is given as drive mode
• But in actual practical situation standby mode
• Here the SOC reduce from 80% to 0% in entire drive mode as shown above plot at stand by modes in between them the SOC remains constant as shown

Test case3:

• Now select test case 3 click
• Run the model and result can be viewed
• All indication are in green indicate no fault conditions are
• Initially cell 2 voltage rises from 3.9V to maximum 4.2V and stabilized to 4.15V cell 1 rises form 3.85V to 4.1V and stabilised to 4.08V
• The battery pack current raising form 0A to30A and start to reduce to 2.5A gradually at end to full charging 2000sec.
• after full charge current flow will be cutoff as show in result plot
• At 2000sec the pack is fully charged to 100%
• After full charge current flow will be cut off as shown in result plot

Question 2:

SOC is defined as the rate of available capacity to its maximum capacity when a battery is fully charged and describes the remaining percentage of the battery

To find this SOC we are using coulomb counting method

The coulomb counting method measures the discharging current of the battery and integrates the discharging current over time in order tp estimate SOC

Which can be estimate from discharging current previously estimate SOC values

SOC(t) = SOC (t-1)+(I(t)/Qn)delta(t).

Modified coulomb counting:

In this technique discharge current is connected with a function and corrected current is found out for accurate SOC estimation

Ic(t) = k2I(t)^2+k1I(t)+k0

Wherek0,k1,k2 are constant values obtained from the particle experimental data

The SOC relation can be given:

SOC (t) =SOC (t-1)+(Ic(t)/Qn)delta(t)

Conclusion:

All the models were explained

https://in.mathworks.com/matlabcentral/fileexchange/72865-design-and-test-lithium-ion-battery-management-algorithms