We developed this web server specifically for protein structure refinement. The energy function is the same as used in the SUMMA server, with an additional step for stereochemistry correction. You can read about it in the 'About' page. It did pretty well in CASP.
http://csb.stanford.edu/kobamin
I would also look at the refinement category of CASP and check out other possible tools.
Hello Siva, you can also use the Refine or Refine2 tools on GalaxyWEB ( http://galaxy.seoklab.org/). Refine has performed very well in CASPs and has been used by many researchers.