Speed sensorless field-oriented control of induction machines using current harmonic spectral estimation

This paper proposes a direct field-oriented controller for induction machine drives based on a new sensorless speed measurement scheme. Current harmonics which arise from rotor slotting and eccentricity are analyzed using digital signal processing techniques. An on-line initialization algorithm determines slot harmonic parameters which depend on machine structural characteristics. A digital spectral estimation algorithm then analyzes multiple current harmonics to produce accurate results at any nonzero speed, independent of time-varying motor parameters. This robust speed information is used to tune the parameters of a mechanical model of the motor and the load. A speed observer based on the mechanical model provides a speed signal to the field-oriented control algorithm. A controller utilizing this tachometer-less observer has the advantage over other sensorless schemes of being able to obtain high accuracy speed information down to very low speeds. This is due to the fact that this scheme does not rely on flux (voltage) measurement, which is significantly degraded at low speed. The algorithm applies to a broad class of induction motors and requires no special machine modifications