Rotor-position estimation for induction machines at zero and low frequency utilizing zero-sequence currents

This paper considers the position and speed estimation at low- and zero-frequency operations in standard delta-connected cage induction machines (IMs). A rotor-slot detection technique is used, where test vectors are injected during the pulsewidth-modulation (PWM) periods and the resulting zero-sequence-current derivatives (ZSCDs) are measured using a nonintegrating Rogowski coil. The rotor slotting in a near-standard 30-kW symmetric IM is utilized for rotor-position tracking. The rotor-slot number was selected to yield a measurable "position-dependent" ZSC. Experimental results show the variation of the measured current signals with rotor position and how these are used for tracking of the rotor position.