Week 7 State of charge estimation

Week 7 State of charge estimation

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

Battery management system: A BMS is an electronic board consisting of a variety of components and circuitry that monitors and regulates internal operational parameters, i.e. temperature, voltage, and current during charging and discharging of the battery. BMS estimates the SOC and SOH of the battery to improve safety and performance. It avoids over-charging and over-discharging of the cells in the battery pack

Simulation file: https://in.mathworks.com/matlabcentral/fileexchange/72865-design-and-test-lithium-ion-battery-management-algorithms

Test dashboard:

This is a BMS modeled using Simulink and Simscape blocks. We can simulate on this model to perform tests for various battery conditions and the response of BMS to the scenario. The dashboard consists of

• BMS_ClosedLoop: It contains the battery and BMS

• Test Sequence Variant: Provides drive input and State conditions

• Lamps: Indicates faults and different conditions

BMS_ClosedLoop:

The BMS closed loop consists of the BMS and the battery plant. There are different cell arrangements in the plant which are selected based on the user-defined state request.

• The operating states are defined by parallel stateflows defined in the ECU.
• The states are standby, driving, charging, and fault.
• The charging state has again 2 substates, CC and CV mode charging.
• The Test Sequence variant subsystem allows the user to select a state request out of 3 defined states.
• Here, the simulation is done for all 3 cases respectively.

Test Case 1:

Test Case 2:

Test Case 3:

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

Coulomb counting: The coulomb counting method measures the discharging current of a battery and integrates the discharging current over time in order to estimate SOC.

We can observe the Coulomb Counting block from the above downloaded model of BMS. The block is constructed using several basic blocks in order to solve an equation to implement the logic of SOC estimation of the battery pack.

• The SOC estimation of a battery pack is done by this above block which solves an equation.
• The active flowing current (amps) is integrated with respect to time to derive the total energy entering or leaving the battery pack.
• Thus follwoing equation is implemented for SOC estimation:

SOC(t) = SOC(t-1) + [I(t) / Qn ] *dt

where , SOC(t) = State of charge of battery pack

I(t) = Discharge current

Qn = Nominal capacity