Zero-sequence Flux and Voltage of Induction Motors Supplied with Low-and High-frequency Currents

In order to precisely define the harmonic content of the main flux and stator voltage of an IM that is fed by high frequency carrier in addition to the normal set of stator voltages, the paper performs the analytical calculation of the zero-sequence components of the air- gap flux and stator voltage. The calculations are performed by defining suitable winding functions to derive the self- and mutual inductances, and by adopting a new inverse air-gap function to model the variation of the saturation level of the machine produced by the additional MMF. Analysis of the calculated expressions, that are confirmed by experimental tests, shows that both zero- sequence flux and voltage include harmonics that can be usefully employed to perform sensorless control techniques. It is also suggested that suitable solutions must be adopted to correctly apply any sensorless method based on zero-sequence signals exploitation.