Low cost efficiency maximizer for an induction motor drive

A method of efficiency maximization is proposed which utilizes sensing of the third-harmonic component of the air gap flux. This signal is used to determine the resulting instantaneous position of the fundamental component of the air gap flux and, consequently, the torque and flux producing components of the stator current. In addition, the third-harmonic signal is also used to determine the rotor speed. Hence, the output of the machine can be calculated with only a single sensor wire attached to the neural point of the machine. The flux producing component can now be readily adjusted to produce the minimum input power for a fixed amount of output power (fixed speed).<>