Sensorless acquisition of the rotor position angle of induction motors with arbitrary stator windings

The anisotropy of a cage rotor is utilized to determine the angular position of the rotor in an induction machine. The switching transients generated by a pulsewidth-controlled inverter serve as test signals. The response of the three-inverter terminal currents is exploited to derive a quasi-instantaneous rotor position signal. The position is sensed at the inverter through the three-phase motor cable by measuring the current derivatives. The method does not require additional wire connections. It is applicable to induction motors having stator windings connected either in wye or in delta. The results are supported by measurements from an experimental setup.