Gaurang,
According to me thje best way to generate sinusoidal waverforms and voltage regulation from 1V to 100V. Motor Generator set with ( Field Controlled By 8051 )or Inverter would also work but will proove expensive.
Almost all voltage stabilizers use variacs. If you have a scrap Voltage stabilizer open it up and check if the variac and the motor controlling variac is still alive. If it is just remove the autotransformer + motor and use it. Usually the motor used is synchronous motor @ 60RPM you can easily control this motor using MICRO to get the desired voltage output you can select the desired voltage within fraction of a second since one complete motor rotation gives you 0V-100V which @ 60RPM will take place in 1s.