Week 7 State of charge estimation

                                                 EV - 21 WEEK - 7

AIM : - 

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

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

EXPLANATION :-

open the document of design and test Li-ion battery management algorithm

download the zip files and extract to the folder consists of these folders are shown below 

open matlab software and open the siulink model file 

open the matlab software and open the BMS closed loop in this block consists of two subsystems 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 are closed loop model are bms_input bms _output , bms_info 

open the simulink model file closed loop BMS harshness dashboard in 

tests.system..BMS.closedloop harshness dashboard model file 

the given open project and model and model in pop -up - dialogue box to install all the model related library files into the current folders and workspace 

Model explantion :-

Test sequence varient 

Manual varient 

BMS_test sequence state request to provide state request commands 

lamps to indicate fault state ,high temperature ,over voltage ,over current ,charging voltage ,sensor operation ,inverter operation ,low temperature , under voltage if any fault in theese red indication will intimate us and all in good condition indicated by green indications 

rotatng switch for manual varient changes while running simulation 

in scope results the SOC of module , module current , individual cell voltage ,individual cell temperature battery cell balancing states are seen as outputs

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 pre change unit charger units are created 

in battery pack two types of configurations as 1 module 6 cells and 16 modules 95 cells 

here we are closing 1 module for lesser simulation runnning time 

TO RUN THE TEST CASES FROM HARNESS DASHBOARD CLOSED LOOP BMS CONTROL :-

we have to test three cases for this model by selecting test sequence varient and select the cases one by one as follows 

TEST : 1 -

select one from test sequence varient dialog box and click apply as shown below 

this selection consists of  selection changes in masked BMS _state request sub system as 

this test consists of the following sequence operation as 

here from the above test sequence editor figure it was set as 

1. driving for 3000secs

2. after 3000 sec starts balancing operations occur for next 1000 sec 

3. then charging and balancing occurs for next 5000 sec 

after that sequence post charge balancing operations occurs till end of the simulation period 

 

run the simulation load results are shown as 

the lamps indications are showing fgreen for overall simulation period showing that there are no faults occur during the sequence from the results we can understand that 

CELL VOLTAGE AND PACK CURRENT :- 

for first 3000 sec 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 3.1V to 3.9V in this range from 3000 to 4000 sec cell balancing occur and this stage the module standby mode and voltage is constant nearly 3.7V

at end of the charging and cell balancing occurs upto 9000 sec after 9000 sec post charge cell balancing starts all cell voltage are balancing to a voltage with respect to cell 1 to 4.1V 

CELL TEMPERATURE :-

initially for 3000sec the temperature range of cells gradually increases from ambient temperature 288k to 302k

the temp of cell is lesser and cell has 6 higher temp of all stages after 4000sec temp start increases exponentially upto constant current region and start reduces as current flow reduces in constant volatge and cell balancing region upto 9000sec 

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

BMS STATE :-

for 3000sec the battery module in drive mode 

from 3000 to 4000 sec the battery module is in balancing standby mode as shown 

after 4000 to 9000sec the battery module is in charging and balancing mode

after 9000sec only post charge balancing mode opeartes upto end of simulation 

SOC :-

initially the state of charge of battery module is in 80% here theyellow plot represents the soc estimation done by coloumb counting technique 

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

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

BALANCING CELLS :-

initially upto 3000sec balancing was not performong after that cell balancing start s with no cell 6 and cell 2as they raised to be shown after this stagecharging and balancing post charge balancing are as occur as cell 6 and cell 2 remain in 1 state still end of the simulatioon 

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

TEST CASE : 2

select one from test sequence varient dialog box and click apply as shown below 

this test case consists of drive mode for 10000 sec and after that charging occurs at the end of the simulation 

now run the model and results can be viewed 

the lamp indication were green for all states which means the model is fault free 

CELL VOLTAGE AND PACK CURRENT :-

the voltage varies from 3.9V to 3.05V in this range from 3000 to 4000 sec cell balancing occur and this stage the module standby mode and voltage is constant nearly 3.7V and the ntire cell is drained upto 8692sec

at end of the charging and cell balancing occurs upto 9000 sec after 9000 sec post charge cell balancing starts all cell voltage are balancing to a voltage with respect to cell 1 to 4.1V 

CELL TEMPERATURE :-

initially for 3000sec the temperature range of cells gradually increases from ambient temperature 288k to 322.5k

the temp of cell is lesser and cell has 6 higher temp of all stages after 4000sec temp start increases exponentially upto constant current region and start reduces as current flow reduces in constant volatge and cell balancing region upto 8692sec 

SOC :-

soc reduces from 80% to 0 cell got fully drained in the drive mode under 8692sec cell balancing not performed here 

TEST CASE : 3 

the test case is 3  selected as shown below in the dialog box and click ok to implement it 

the test case is altered to third as shown

the test consists of charging for entire duration of time

run the model and results can be viewed 

CELL VOLTAGE AND PACK CURRENT :- 

initially cell 2 voltage rises from 3.9 to maximum 4.2V 

cell 1 rises from 3.85 to 4.1V and stabilised the battery pack current raising from 0A to 30A and start to reduce to 2.5A gradually at the end of the full charging 2000sec after full charge current flow will be cut off as show in result plot 

CELL TEMPERATURE :-

the cell temp continue to increase heat upto full charge and after that the temperatures get started to reduce to ambient temperature 

as shown from result plot the temperature start decreses after full charger 

BMS STATE : - the entire battery pack operating in charging mode as shown above 

SOC :-  the pack soc gets 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 

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

The coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC. Coulomb counting method is done to estimate the SOC, which is estimated from the discharging current, I batt, and previously estimated SOC values

SoC Estimation by Coulomb Counting is based on the measurement of the current and integration of that current over time

Coulomb counting gives a relative change in SoC and not an absolute SoC. If you measure the current over a given time step you have a measure of the number of Ah that have left or been received by the battery.

where:

• SoC(t) = estimated State of Charge at time, t
• SoC(t-1) = previous State of Charge at time t-1
• I(t) = charging or discharging current at time, t
• Q_n = battery cell capacity
• Δt = time step between t-1 and t

If you want to know the absolute SoC you need to know the starting SoC of the cell, SoC(t-1) as given in the equation. One option is to fully charge the cell to a known voltage. Charging to maximum cell voltage and SoC can be used as a reset and known point.

SOC ESTIMATION IN BMS MODEL :- 

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

here the discharge current from battery given to the gain value as 1/3600 to convert current Ahr 

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 to 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 implements the coulomb counting for soc estimation are explained clearly and succesfully