Sensorless flux position estimation at low and zero frequency by measuring zero-sequence current in delta connected cage induction machines

This paper considers the estimation of both flux and rotor position in delta-connected cage induction machines operating at low and zero frequencies. It is shown that the variation of leakage inductance due to either saturation or rotor slotting can be tracked by measuring the derivative of the zero-sequence current in response to the application of appropriate voltage test vectors. The method requires access to the machine phase windings but needs only a single extra sensor, in the form of a nonintegrating Rogowski coil, which measures directly the zero-sequence current derivative. In this paper, experimental results are presented for the tracking of flux position.