Week 7 State of charge estimation
the first step is to click the link and download the file
extract the file and open BAttery system.prj
TEST-1
The Test Sequence variant contains 3 tests this is test 1 you can see all lights GREEN this indicates everything is proper and working within limits if the lights would be RED there will be a FAULT in that system
after running TEST_1 we get following graph
in Cell voltage we can see all cells are in driving so DIscharging is happening
after that stand by mode
after that charging is happening so voltage is increasing
in temperature graph we can see when driving cell temperature is increasing then decreasing
while driving SOC decreases and while charging SOC starts increasing initially the SOC is at 0.8 which is 80% and goes down upto 0.45 which is 45%
in TEST-2
in TEST-2 there is fault in BMS state and temperature of cell is also high which is concering
The Cell_temperature goes from 290 to 323 and then drops
SOC goes from 0.8 or 80% to 0.35(35%) and then goes up
in TEST-3
we can see that all lights are GREEN therefore there is no faulty condition
in TEST_3 we can see
it is charging in BMS state
Therefore SOC is inreasing from 0.8(80%) to 1(100%)
after fully charged TEmperature also starts dropping after 2000 seconds which means battery fully cahrged
the Pack_current rises from 0 to 30 A and after fully charging the battery pack it cuts off
The BMS_closed loop contains 2 blocks which are BMS ECU and PLANT
PLANT contains all cells
where as ECU contains
Coulomb counting:
SOC(State Of Charge) 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 capacity
Coulomb Counting Method
The Coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC [20]. Coulomb counting method is done to estimate the , which is estimated from the discharging current, , and previously estimated SOC values, . SOC is calculated by the following equation:
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
To improve the Coulomb counting method, a new technique called modified Coulomb counting method is proposed. 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 experimental data, corrected current is calculated by the following form:where , and are constant values obtained from the practice experimental data.
In modified Coulomb counting method, SOC is calculated by the following equation:
The experimental results show that the accuracy of the modified Coulomb counting method is superior to the conventional Coulomb counting method.