Induction motors are the most widely used electrical motors due to their reliability,
low cost and robustness. However, induction motors do not inherently have the capability
of variable speed operation. Due to this reason, earlier dc motors were a
pplied in most of
the electrical drives. But the recent developments in speed control methods of the induction
motor have led to their large scale use in almost all electrical drives.
Out of the several methods of speed control of an induction such as pole changing,
frequency variation, variable rotor resistance, variable stator voltage, constant V/f control,
slip recovery method etc, the closed loop constant V/f speed control method is most widely
used. In this method, the V/f ratio is kept constant which in turn maintains the magnetizing
flux constant so that the maximum torque remains unchanged. Thus, the motor is
completely utilized in this method.
