For the variable speed in automatic control, this paper describes, at first, performance equations of an induction motor which has the free rotating stator. This motor with rotating stator has a speed control factor itself by equivalent variable frequency in stator side. Secondly, an additional invertor source on the rotor slip ring serves the purpose of improving the speed control factor. The advantages decribed above permit to control the speed continuosly from zero to maximum allowable speed with low energy of thyristor a feed-back device may be used for speed stabilization under variable load.