After converting drawing in Microstation (3D) Inventor can not read the new drawing

Good morning all,

I am new in this forum and working for a support department. One of our designers asked me to work out how to convert an drawing in Microstation for using in Inventor. Under this line I copy the fully question. The answer of the specialist was to look for a solution in Bentley.

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Our designers converting drawings from Microstation (3D) to Inventor and can not read the new drawings.
No step files are available created bij Microstation. Converting to DWG 3D was an option but there they missed the volume structure of the entities. They were a polyfaces.
Polyfaces give the impression that this is a volume but actually this is an empty box.
We needed a solid.
The result is that when you create a sat-file in autocad of such a drawing, it does not recognize these polysurfaces and therefore cannot convert to the sat-file.
Sat- files can be imported in Inventor.

We look for a good working solution to handle this files.