Analysis and Compensation of Saliency Harmonic Components in Multi-Salient Induction Motors for Encoderless Speed Control

Induction motors usually present multiple spatial saliencies that contain useful information about the spatial magnetization and geometric state of the rotor. Each saliency modulates the transient leakage inductance producing periodical variations in the transient stator current response. A robust method to access the transient leakage inductance consists of exciting the motor with voltage pulses and computing a current slope on the measured resulting stator currents. Due to the parallel connection of the transient leakage inductances during active inverter switching, additional saliency harmonic products appear in the measured phase current responses, which have not been researched so far in literature. These saliency harmonics products can have relevant amplitudes depending on the motor construction and operating point, and possess deterministic frequencies that are related to the motor saliency frequencies. In this work, saliency harmonic products will be mathematically analysed for a star-connected induction motor for a voltage step excitation method. For a precise saliency separation, it is meaningful to compensate the saliency harmonic products. Experimental results will show the emergence of several saliency harmonic products at high loads, and will show an improvement in the rotor position estimation accuracy when such harmonic products are compensated.