A Slot Harmonic Detection with an Empirical Formula to Extend the Speed Range Control in 3-Phase IM Drives

摘要

A lot of development has been made in the area of sensorless speed measurement in Induction Motor (IM) where the tachometer is discarded and the speed is measured from the magnetic characteristics of the machine itself. In IM there are slots of the surface of the stator and rotor iron cores. When the rotor rotates, harmonics are produced in the air-gap flux that induces slot harmonic voltages in the stator windings. By measuring either the magnitude or frequency of the slot harmonics the rotor speed can be determined. A method of improving the performance of a system using the rotor slot harmonic technique is investigated. This involves the use of an empirical formula to estimate the rotor speed, based on current and frequency readings. This is used in the speed range where the rotor slot harmonics become difficult to detect.