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

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