Creating a PWM controller

Hello, I am currently working on a project with several people and my task is to understand a Simulink model and modify it to simulate a PWM controller.

Here are the diagrams of the given model (see pictures) and after all that there is to modify, among the instructions that were given to me I could understand that the "DC source voltage" represents the solar panel and that the "PWL voltage source" represents the battery that I must power. So my question is: what value should I enter in the "Voltage-controlled Switch"?

The solar panel voltage varies up to a maximum of 23V and the battery voltage must be 12V.