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)
MATLAB AND SIMULINK
1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results.
MODEL:1
A:click on test sequence varient block.
then select test case as 1.
Now, click on BMS state request block.
we get below chart.
from the above fig we observe that,driving is for 3000sec then followed by balancing for 1000 sec followed by charging and balancing for 4000 seconds, then there is post charge balancing.
by running the simulation.
RESULTS:
1)The first plot shows the individual cell voltages the voltage fluctuates between 3.2 and 3.7 volts between 0 to 3000 seconds.
the nominal voltage of each cell is 3.7 volts and it decreases to 3.2 volts.fluactuates in cell voltage from 0 to 3000 seconds shows that the vehicle is driving in driving mode from 3000 to 4000 seconds we have balancing mode.thus, cell voltage gets balanced to 4 volts till 4000 seconds.from 4000 to 8000 seconds there is charging and balancing state.thus, cell voltage rises to 4.2 volts.
2) Entire battery pack current is shown in pack current graph.as the current decreases while charging thus the current is -60A from 0to 3000 seconds. now from 3000 to 4000seconds,there is cell balancing ,thus pack current reduce to 0A. and from 4000 to 8000 seconds , there is charging state, thus the current increases to 30a.then occur post charge blancing, thus pack current comes to 0A.
3) The third graph is cell temperature graph.
the cell temperature increases in driving stage as vehicle is in driving mode then during balancing stage,cell temperature reduces and then at start of charging.
the temperature increases suddenly then later at charging and post charge balancing, the cell temperature shows the reducing behaviour.
4) The BMS state graph shows that during 0 to 3000 seconds shows that the vehicle is in driving mode from 3000 to 4000 seconds,we have stand by mode from 4000 to 8000 seconds, there is charging state.
5) The SOC graph tells that,
during driving state, the SOC reduces from 80% to 45%
during balancing state,SOC remsains constant at 45%
during charging state, the SOC increases to 100% and then remains constant.
6)The cell balancing signal is shown in the balance command graph.
B: Now select test case as 2.
the driving state is for 0 to 1000 seconds. thn charging state occurs.
1) The cell voltage varies till 2000 seconds and then remains constant.
2)At start the pack current increases to 30A and then reduce to 0A at 2000 seconds and then remains constant at 0A.
3)cell temperature varies as shown in graph.
4) as there is only charging state, thus BMS graph shows BMS charging.
5) as only charging takes place.
thus,SOC was 80% at first, then SOC increases to 100% in 2000 seconds then SOC remains constant at 100%.
2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?
COULOMB COUNTING: The SOC is one of the most important parameters for batteries. in general the SOC of a battery is defined as the ratio of its current capacity(Q(t)) to the nominal capacity(Qn). the nominal capacity is given by the manufacturer and represents the maximum amount charge that can be stored in the battery.
The SOC can be defined as follows:
SOC(t)=Q(t)/Qn
The varrous mathematical methods of estimation are classified according to methodology. the classification of these SOC estimation methods is divided in to the following four categories.
i) Direct measurement : this method uses physical battery properties, such as the voltage and impedance of the battery.
ii) Book keeping estiation: this method uses discharging current as the input and integrates the discharging current over time to calculate the SOC.
iii)Adaptive systems: the adaptive systems are self designing and can automatically adjusts the SOC for different discharging conditions. various new adaptive ssystems forSOC estimation have been developed.
iv)Hybrid methods: the hybrid models benefit from the advantages of each SOC estimation method and allow a globlly optimal estimation performance. the literature shows that the hybrid methods generlly produce good estimation of SOC, compared to individual method.
BOOK KEEPING ESTIMATION:
Book-keeping estimation method uses battery discharging current data as input. This method permits to include some internal battery effects as self-discharge, capacity-loss, and discharging efficiency.
COULOMB COUNTING METHOD:
The coulomb counting method measure the discharging current of a battery and integrates the discharging current over time in order to estimates SOC. coulomb counting method is done to estimate the SOC(t), which is estimates fro the discharging current,I(t) and previously esstimated SOC values,SOC(t).
SOC is calculated by the following equation:
SOC(t)=SOC(t-1)+I(t)/Qn *theta t
But ,there are several factors that affect the accuracy of coulomb counting method including temperature, battery history,discharge current and cycle life.
MODIFIED COULOMB COUNTING METHOD:
The modified Coulomb counting method uses the corrected current to improve the accuracy of estimation. The corrected current is the function of discharging current. There is a quadratic relationship between the corrected current and discharging current of battery.
by practice of experimentation data, corrected current is calculated by following terms
Ic(t)=K2I(t)^2+K1I(t)+Ko,
where K2,k1, k0 are constant values obtained from the practice experimentation data.
in modified coulomb counting method,SOC is calculated by following equation
SOC(t)=SOC(t-1)+Ic(t)/Qn * theta t
the experimental results shows that the accuracy of the modified coulomb counting method is superior to the conventional coulomb counting method..
3. To compute the SOC of battery, insert a plant block into the model.
BMS algorithm models, protects, reports the measurement from battery pack.
by clicking on the current power limit calc block.we get following block diagram as shown.
here, the cell voltage and cell temperature is used to decide maximum allowable charging and discharging current limits.
when cell is at lowest SOC, its voltage is low, and thus it is important to prevent cell from delivering large amount of current because it will cause large voltage drops that could be potential below the cut off voltage specify by the cell manufacture.
click on discharge current limit calculate block.
we get following block diagram shown.
here, by comparing the minimum cell voltage in the module against this lowest threshold voltage aand then divided by maximum internal cell resistance value,we can compute the voltage based threshold.
It is also important to limit the current delivery and current intake when temperature is too high or too low.
using the lock up table with rising and falling s shape profile, we can specify current threshold based temperature an thus can modulate allowable current delivery.
it is recommended to avoid low and high temperature during discharging and low tempearture during charging.
then the above two threshold are then compared and minimum of this two becomes the current limit.knowing how much longer we can be able to drrive our car before we had stop for recharge depends on the accurate estimation of battery SOC.In battery systems, we don not measure SOC directly, we actually measure something else aand then relate it with SOC.
3 methods are used for SOC estimation.
but, coulomb counting is mostly used.by clicking on the estimation block we get the below block diagram.
In this coulomb counting method, the entering and leaving currents of the cell are integrated to track the safe chargable time.
here the two input signals current and temperature are taken.
the current ssignal goes to gain block and the tempearture signal goes to current look up table.
then, as seen signalsare multiplied and divided as shown and then output is given to discrete time integrator to track the safe chargable time and then SOC is estimated.
advantage of coulomb counting method is its simplicity an low computational cost.
the draawback coulomb counting method is aaccumulation of current sensor error and inability to recover fromwrong initial condition because of lack of feedback from voltage measurement.
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)
MATLAB AND SIMULINK
1.Simulate the 3 test cases from harness dashboard and write a detailed report on the results.
MODEL:1
A:click on test sequence varient block.
then select test case as 1.
Now, click on BMS state request block.
we get below chart.
from the above fig we observe that,driving is for 3000sec then followed by balancing for 1000 sec followed by charging and balancing for 4000 seconds, then there is post charge balancing.
by running the simulation.
RESULTS:
1)The first plot shows the individual cell voltages the voltage fluctuates between 3.2 and 3.7 volts between 0 to 3000 seconds.
the nominal voltage of each cell is 3.7 volts and it decreases to 3.2 volts.fluactuates in cell voltage from 0 to 3000 seconds shows that the vehicle is driving in driving mode from 3000 to 4000 seconds we have balancing mode.thus, cell voltage gets balanced to 4 volts till 4000 seconds.from 4000 to 8000 seconds there is charging and balancing state.thus, cell voltage rises to 4.2 volts.
2) Entire battery pack current is shown in pack current graph.as the current decreases while charging thus the current is -60A from 0to 3000 seconds. now from 3000 to 4000seconds,there is cell balancing ,thus pack current reduce to 0A. and from 4000 to 8000 seconds , there is charging state, thus the current increases to 30a.then occur post charge blancing, thus pack current comes to 0A.
3) The third graph is cell temperature graph.
the cell temperature increases in driving stage as vehicle is in driving mode then during balancing stage,cell temperature reduces and then at start of charging.
the temperature increases suddenly then later at charging and post charge balancing, the cell temperature shows the reducing behaviour.
4) The BMS state graph shows that during 0 to 3000 seconds shows that the vehicle is in driving mode from 3000 to 4000 seconds,we have stand by mode from 4000 to 8000 seconds, there is charging state.
5) The SOC graph tells that,
during driving state, the SOC reduces from 80% to 45%
during balancing state,SOC remsains constant at 45%
during charging state, the SOC increases to 100% and then remains constant.
6)The cell balancing signal is shown in the balance command graph.
B: Now select test case as 2.
the driving state is for 0 to 1000 seconds. thn charging state occurs.
1) The cell voltage varies till 2000 seconds and then remains constant.
2)At start the pack current increases to 30A and then reduce to 0A at 2000 seconds and then remains constant at 0A.
3)cell temperature varies as shown in graph.
4) as there is only charging state, thus BMS graph shows BMS charging.
5) as only charging takes place.
thus,SOC was 80% at first, then SOC increases to 100% in 2000 seconds then SOC remains constant at 100%.
2.What is coulomb counting? Refer to the above model and explain how BMS implements coulomb counting for SOC estimation ?
COULOMB COUNTING: The SOC is one of the most important parameters for batteries. in general the SOC of a battery is defined as the ratio of its current capacity(Q(t)) to the nominal capacity(Qn). the nominal capacity is given by the manufacturer and represents the maximum amount charge that can be stored in the battery.
The SOC can be defined as follows:
SOC(t)=Q(t)/Qn
The varrous mathematical methods of estimation are classified according to methodology. the classification of these SOC estimation methods is divided in to the following four categories.
i) Direct measurement : this method uses physical battery properties, such as the voltage and impedance of the battery.
ii) Book keeping estiation: this method uses discharging current as the input and integrates the discharging current over time to calculate the SOC.
iii)Adaptive systems: the adaptive systems are self designing and can automatically adjusts the SOC for different discharging conditions. various new adaptive ssystems forSOC estimation have been developed.
iv)Hybrid methods: the hybrid models benefit from the advantages of each SOC estimation method and allow a globlly optimal estimation performance. the literature shows that the hybrid methods generlly produce good estimation of SOC, compared to individual method.
BOOK KEEPING ESTIMATION:
Book-keeping estimation method uses battery discharging current data as input. This method permits to include some internal battery effects as self-discharge, capacity-loss, and discharging efficiency.
COULOMB COUNTING METHOD:
The coulomb counting method measure the discharging current of a battery and integrates the discharging current over time in order to estimates SOC. coulomb counting method is done to estimate the SOC(t), which is estimates fro the discharging current,I(t) and previously esstimated SOC values,SOC(t).
SOC is calculated by the following equation:
SOC(t)=SOC(t-1)+I(t)/Qn *theta t
But ,there are several factors that affect the accuracy of coulomb counting method including temperature, battery history,discharge current and cycle life.
MODIFIED COULOMB COUNTING METHOD:
The modified Coulomb counting method uses the corrected current to improve the accuracy of estimation. The corrected current is the function of discharging current. There is a quadratic relationship between the corrected current and discharging current of battery.
by practice of experimentation data, corrected current is calculated by following terms
Ic(t)=K2I(t)^2+K1I(t)+Ko,
where K2,k1, k0 are constant values obtained from the practice experimentation data.
in modified coulomb counting method,SOC is calculated by following equation
SOC(t)=SOC(t-1)+Ic(t)/Qn * theta t
the experimental results shows that the accuracy of the modified coulomb counting method is superior to the conventional coulomb counting method..
3. To compute the SOC of battery, insert a plant block into the model.
BMS algorithm models, protects, reports the measurement from battery pack.
by clicking on the current power limit calc block.we get following block diagram as shown.
here, the cell voltage and cell temperature is used to decide maximum allowable charging and discharging current limits.
when cell is at lowest SOC, its voltage is low, and thus it is important to prevent cell from delivering large amount of current because it will cause large voltage drops that could be potential below the cut off voltage specify by the cell manufacture.
click on discharge current limit calculate block.
we get following block diagram shown.
here, by comparing the minimum cell voltage in the module against this lowest threshold voltage aand then divided by maximum internal cell resistance value,we can compute the voltage based threshold.
It is also important to limit the current delivery and current intake when temperature is too high or too low.
using the lock up table with rising and falling s shape profile, we can specify current threshold based temperature an thus can modulate allowable current delivery.
it is recommended to avoid low and high temperature during discharging and low tempearture during charging.
then the above two threshold are then compared and minimum of this two becomes the current limit.knowing how much longer we can be able to drrive our car before we had stop for recharge depends on the accurate estimation of battery SOC.In battery systems, we don not measure SOC directly, we actually measure something else aand then relate it with SOC.
3 methods are used for SOC estimation.
but, coulomb counting is mostly used.by clicking on the estimation block we get the below block diagram.
In this coulomb counting method, the entering and leaving currents of the cell are integrated to track the safe chargable time.
here the two input signals current and temperature are taken.
the current ssignal goes to gain block and the tempearture signal goes to current look up table.
then, as seen signalsare multiplied and divided as shown and then output is given to discrete time integrator to track the safe chargable time and then SOC is estimated.
advantage of coulomb counting method is its simplicity an low computational cost.
the draawback coulomb counting method is aaccumulation of current sensor error and inability to recover fromwrong initial condition because of lack of feedback from voltage measurement.