Field acceleration method (FAM) is the target state variable of the field acceleration method is induction motor torque. In FAM theory, co-ordinate transformation is not involved. It attempts to avoid electromagnetic transients which cause delay in torque control response. First, electromagnetic transients of three-phase induction motor are analyzed. Initial attempt is made to derive `equivalent circuits valid for both steady state and transient states in induction motor.
The key point of FAM control is that the exciting current is kept constant in magnitude and continuous in the equivalent circuit. The speed of rotating air gap flux is made free or adjustable. This means that the magnetic field in the air gap is kept constant in its amplitude and that its speed is adjustable so that a desired value of torque is produced. When the air gap flux is kept constant, other variables like voltages, current and torque are functions of slip frequency only. By accelerating or decelerating rotation of the air gap flux to choose the slip frequency, the torque can be controlled as desired.
