CCCV Charging of Li-ion batteries connected in parallel
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I am simulating the CCCV charging of a 2s4p battery pack. There are lot of fluctuations in the voltage, current during CCCV charging (see the attached pic).
I tried using the TUNE in PID controller, but it is not taking the plant
I have attahced all the relevant files.
How can I rectify this
Your support will be of great help for me.
Joel Van Sickel on 16 Feb 2023
That behavior is caused by the fact that you switch to a hard coded constant current reference whenever the V_Highest is less than V_top. Since you have tracking turned on for your PID, every time you briefly jump to this set point, the controller resets to this point as well, and then has to lower again. The problem isn't your gains, the problem is your logic in determining when to switch between the PID logic and the PID controller. Also, it can't tune your system because it is a discontinuous system with discrete switching devices. You'd have to use a frequency response estimation to use the tune function. You will likely need to manually tune the PI values and be more careful about when you switch between the closed loop controller and the fixed constant current reference.
Essentially, your PI controller is working, because it is trying to reduce the difference between V_highest and V_top, Which it is doing, but whenever it gets them close, it triggers the logic to 'reset' the controller (switch to the constant value reference which, because tracking is on the PID, 'resets' it), and it has to start over.