When SDRAM initializes the module simulation, other modules are used. If the compilation is correct, the simulation will report an error:
Instantiation of ‘sdram_model_plus’ failed. The design unit was not found.

Solution:

Add files at the same time, and the name is the same to the tb file.

If you don’t find the file, you can add one of them. Just note that the name in the red box above is the same to the tb file.