Week 7 State of charge estimation
1.
The 3 simulink models Battery_Model,BMS system and BMS_ClosedLoop_Harness_Dashboard are opened.
This is the harness dashboard simulink model.
In this model,different test cases can be simulated by selecting the number of test case in the test sequence variant block and running the model.
1.
This is the simulink model after running the first test case.
Here all the indicators are green so there is no error.
this is the scope obtained after running the first case-
The graphs shows that the battery temperature increases in driving and charging. SOC decreased up to 50% in driving condition and it was increased while charging.Battery voltage was increased to 4.2V while charging.
2.
This is the simulink model after running the second test case.
This shows that some fault condition has occured,since the indicator has become red.
this is the scope obtained after running the second case-
Due to the fault condition occured in second case, even after charging was started, the soc did not increase. It continues to decrease.
3.
This is the simulink model after running the third test case.
this is the scope obtained after running the third case-
The soc reached 100% in charging and remained in stand by mode. Cell temperature also decrased when standby mode was acheived.
2.
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(t), 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.
The simulink model also implements this coulomb counting method .
In the BMS_ClosedLoop model,double click on the BMS ECU
In the BMS ECU,double click on the SOC_Estimation block
In the SOC_Estimation block,Double click on the coulomb counting block
In the coulomb counting block,which is given below the process of coulomb counting can be seen.
Temperature and current from the battery is given as inputs.Current signal is given to a gain block and temperature is given to capacity look up table since it varies according to temperature.This current output is given to another block where it is divided by capacity.These inputs are given for integration .Hence the SOC is estimated.