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This paper considers both flux and rotor position estimations for sensorless control of delta-connected cage induction machines (IMs) at low and zero frequency operation. The variation of leakage inductance due to either saturation or rotor slotting is tracked by measuring the derivative of the zero sequence current in response to the application of appropriate voltage test vectors. The method requires only a single extra sensor. It requires access to machine phase windings and is appropriate for integrated-type induction motor drives. Both a closed-slot and an open-slot machine is used to demonstrate rotor flux and rotor position tracking, respectively. Experimental results are presented showing sensorless torque control and sensorless speed and position control at low and zero frequencies. Index Terms--Induction machine, position estimation, rotor slotting saliency, saturation saliency, sensorless control, zero sequence current.

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 non-integrating 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. Index Terms--Induction machine (IM), position estimation, rotor-slotting saliency, sensorless control, zero-sequence current (ZSC).

This paper describes a new method for estimating the incremental rotor position for an induction machine without using a shaft sensor. The method assumes a saturated induction motor having an engineered cage saliency spanning one pole pitch. The voltage-source inverter driving the machine is also used to inject a high-frequency signal which is needed to detect position. The paper discusses two ways in which this can be achieved. This method has been proven successful with a loaded machine at low speeds and overcomes problems associated with saturation. Index Terms - Induction motor drives, sensorless position control, vector control.