Sensorless vector control at low and zero frequency considering zero-sequence current in delta connected cage induction motors

This paper considers rotor flux tracking 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 non-integrating Rogowski coil, which measures directly the zero-sequence current derivative. In this paper, experimental results are presented for the tracking of flux position and sensorless torque control.