Electric motors are controlled according to different aspects depending on the specific applications they have in different systems. Start-up, speed control, position control and braking are the control aspects of an electric motor, for which a control method is considered depending on the intended application. A three-phase induction motor is essentially a constant speed motor. However, due to changes the mechanical load, changes in rotor rotation speed are inevitable. Therefore, it is somewhat difficult to control its speed. Induction motor speed control is accomplished at the cost of reduced efficiency and low power factor. In this paper, all methods of speed control of induction motors are examined in detail. By examining conventional methods, their advantages and disadvantages are reviewed. پرونده مقاله