The question is unclear. What do you want particularly to improve? The electrical efficiency of modern VFD is very high, e.g. 98 %. It can be still interesting to improve it, but it's a matter of profound power electronics experience and hardly suitable for an academic project.
You get probably a much higher efficiency saving potential by adjusting the VFD voltage characteristic according to the application parameters, e.g. to choose a quadratic characteristic instead of the default linear V/f characteristic for a fan or centrifugal pump drive.