Week 7 State of charge estimation

State of charge estimation

Aim:

1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results

2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?

Hint :(Download the file from the link and go to SOC estimation model-ECU block)

Model explanation:

• Dash board

1. Test sequence variant
2. Manual variant
3. BMS Test sequence state request to provide state request commands
4. Lamps to indicate fault state high temperature, over current, charging voltage, sensor operation, low temperature, under voltage. If any fault in these read induction will intimate will intimate us and all in good conditions indicated by green indication.
5. Rotating switch for manual variant changes while running simulation
6. In scope results the SOC of module, module current, individual cell voltage, individual cell temperature battery state cell balancing states are seen as outputs

• BMS Closed Loop:

In this main block consist 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 plant unit the battery pack unit Per charger unit charger /load units are created

In battery pack there are two types of configuration as 1 module 6 cells and 16 modules 95 cells

Here we are closing 1 module for lesser simulation running time

1. 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 and click apply as shown below

This selection consists of selection changes is marked BMS state request subsystem as

This test case consist of the following sequence operation as

Here from the above test sequence editor fiqure it was set as

1. Driving for first 3000 secs
2. After 3000 sec starts balancing operations occur for next 1000 secs
3. Then charging and balancing occurs for next 5000 secs
4. After that sequence post charge balancing operation occurs till end of the simulation period

Run the simulation land result are shown as:

The lamp indication are showing green for overall simulation period showing that there are no faults occurs during the sequence

From the result we can understand that

Cell voltage and pack current:

For first 3000 secs all 6 cells are drive model where discharging occur majorly and in stand by 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 upto 9000sec. after 9000sec post charge cell balancing a starts all cell voltage are balancing to a voltage with respect to cell 1 to 4.1V shown

CELL Temperature:

Initially for 3000sec the temperature range of cells increase gradually from ambient temperature 288k to 302k

The temperature of cell is lesser and cell 6 has higher temperature for all stages after 4000sec temperature start increase exponentially upto constant voltage and cell balancing region upto 9000sec

Cell 1max temperature raised upto 302k and cell 6 temperature raised upto 317k after 9000sec the temperature still reduce and remains stable at reaching ambient temperature

BMS state:

For 3000sc the battery module in drive mode

From 3000sec to 4000sec the battery module in balancing stand by mode as shown

After 4000sec upto 9000sec the battery module in charging and balancing mode

After 9000sec only post charge balancing mode operates upto end of simulation

SOC:

Initially the state of charge of battery module is in 80% here the yellow plot represent soc estimation done by coulomb counting technique

Blue plot represent SOC estimation using unscented Kalman filter technique Red plot represents SOC estimation using extended Kalman filter technique among three UKF &EKF technique estimate accurately than coulomb counting technique

Initially for 3000sec SOC decreases to nearly 45% during drive mode after 3000sec upto 4000sec the SOC is constant 45% cell balancing occur in standby mode

From 4000sec to 9000sec module in charging mode after 9000sec the SOC between constant approximately 94% as seen from above plots

balancing cells:

initially upto 3000sec balancing as not performing after 3000sec cell balancing starts with on cell 6 and cell 2 as they rised to as shown. After this stage charging and balancing post charge balancing are occur as cell 6 and cell 2 remain in 1 state still end of simulation

as well is in lesser voltage than other cells it remains in 0 state through out the simulation all cell voltage try to balance equally as we seen earlier in signal cell voltage plot

TEST case2:

Now select test case 2 and click apply in test sequence variant dialog box shown

The case altered to second shown

This test case consist of drive mode for 10000sec and after that charging occur till end of simulation

Now run the model and result can be viewed

Dashboard result are shown

The scope result plotted as

Cell voltage and pack current:

The cell voltage varies from maximum 3.9V and reduce to 3.05V as cut off voltage up to 9000sec entire capacity drained at 9000sec. the pack current discharge up to maximum 70A and slight charging occur during the over all drive. Some stand by mode conditions are in between the drive mode

Cell Temperature:

Here cell 1 lesser temperature variant from 288K to approximately 302.5K cell 6 in having temperature variant from 288K to approximately 322.5K. the cell temperature are slightly reducing in between drive mode as these duration are in stand by

Battery Module State:

Entire sequence is performing in drive mode as shown the plot. Small duration of stand by modes are not ploted in this plot a simulation 10000sec command is given as drive mode

But in actual practical situation stand by mode are present battery current drains by other small of EV’s

SOC of Module:

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

Balancing:

Here balancing of cells are not performed as shown as balance states are in0 for entire drive mode

Test case3:

Now select test case 3 click apply in test sequence variant dialog box as shown below

The test case is altered to third as shown

This test case consists of charging for entire duration of time

Run the model and result can be viewed

All indication are in green indicate no fault conditions are occur

The plots are shown as

Cell voltage and pack current:

Initially cell 2 voltage rises from 3.9V to maximum 4.2V and stabilised 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

Cell voltage and pack current:

Initially cell2, voltage rises from 3.9V to maximum 4.2V and stabilised to 4.15V

Cell rises from 3.85V to 4.1V and stabilised to 4.08V

The battery pack current raising from 0A to 30A and start to reduce to 2.5A gradually at end to full charging upto 2000ses.

At 2000sec the pack is fully charged to 100%

After full charge current flow will be cut off as shown in result plot

Cell Temperature:

The cell temperature continue to increase heat upto full charge and after that the temperature gets started to reduce to ambient temperature

As shown from result plot the temperature start decrease after full charger

BMS state:

Entire battery pack sequence is operating in charging mode as shown above

SOC:

The pack SOC gets fully charged at 2000sec and remains at full charge for rest of the sequence as shown above

The actual state of charge is around 93% shown as full charge shown by UKF and EKF techniques

Cell balancing:

Here form 0sec the cell 6 and 2 starts to balance with respect to cell 1 and all cells are try to balancing at end of simulation

Hence from above three test cases the performance of BMS on various factors are discussed and analysed

1. To explain coulomb counting for finding the SOC estimation in BMS:

Coulomb counting:

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)

SOC estimation is BMS model:

To see model of coulomb counting technique in BMS model click the subsystem of SOC estimation and click coulomb counting

Here the discharge current from battery given to gain with value as 1/3600 to convert current to Ah

The value is divided by capacity due to temperature change then integrated with a gain value of 1 with sample time 1 as we are using discrete integrator

We will get the SOC value from 0 to 1 multiple with 100 get in percentage of SOC

Conclusion:

Simulate the 3 test cases from harness dashboard and write a detailed report on the results refer to the above model and explain how BMS implement coulomb counting for SOC estimation are explained clearly and sussesfully