Table-based battery sometimes stops charging

Hello,

I am currently working on a Simulink/Simscape model to model a battery cell stack using only the provided datasheet from the battery manufacturer. The charging normally works fine but sometimes after reaching an SOC above 90% the battery doesn't charge anymore and the current measured peaks to a positive and instantly drops to zero. It is quite strange as when I run the same simulation various times the problem appears at different SOCs when using the same or different charging currents.

Before this happens, a warning appears that the maximum terminal voltage is exceeded even though I limit the charging voltage that the ideal charger uses to the maximum voltage of the battery cell stack.

It would mean the world if somebody could help me in this problem

Answer 1

[Abhas]

Hi Diogo,

When addressing such scenarios in which terminal voltage exceeds the maximum allowed value during the charging process, which can cause the current to drop to zero unexpectedly, you should follow the below steps:

1. Check Terminal Voltage: Ensure that the terminal voltage of your battery does not exceed the maximum specified in the datasheet. The terminal voltage is a combination of the "open circuit voltage" (OCV) and the voltage drop due to the internal resistance of the battery. You can monitor this in your simulation to see when and why it exceeds the limit.
2. Implement a CC-CV Charging Strategy: To keep the terminal voltage within your desired range, you can use the Simscape Battery (CC-CV) blocks. These blocks are great because they implement a constant voltage step, allowing the battery to charge fully while gradually reducing the current. This should help prevent the voltage from exceeding your set limits.
3. Review Initial Conditions: Double-check the initial conditions set in your model. If both initial "SOC" and initial voltage are defined, it might lead to conflicts. It's often best to define one and let the model compute the other based on the battery characteristics.

You may refer to the following MathWorks documentation links to have a better understanding on Simscape battery blocks and their modeling with Simscape:

1. https://www.mathworks.com/help/simscape-battery/create-battery-pack.html
2. https://www.mathworks.com/help/simscape-battery/ref/batterycccv.html