The magnetomotive force or mmf is a measure of the strength of a magnetic field. Moreover, the mmf is proportional to the number of turns in a coil and the current that flows through this coil. Thus, the measure of the mmf in a coil is the ampere-turn or just AT of that coil. Thus, 1AT represents 1A circulating in one turn of a coil. Accordingly, more current implies a stronger magnetic field, and more turns also yields stronger magnetic field.
where t is time, ω is the angular frequency (velocity) in electrical radians /sec, θ is angular displacement of the rotor in electrical radians, and Fmax is the peak value of the fundamental component of the mmf, which is given by the following
The torque in an induction motor is produced from the interaction of the resultant air gap flux and the mmf (magnetomotive force) of either the stator winding or the rotor cage . Torque is produced on the shaft of the motor only if the rotor is running at a speed lower than the synchronous speed, i.e. if the slip speed is a nonzero value. Many expressions can be used to compute the torque of an induction motor [39, 43]. Here, the following expression can be used to compute the so-called air gap torque profile