A new type of harmonic-current-excited brushless synchronous machine with open windings

In an open-winding machine, the three-phase stator currents can be controlled to contain the same harmonic current components like the third harmonics. This paper introduces a new harmonic current excitation principle in synchronous machines based on open winding controls. Unlike existing harmonic excitation technologies which utilizing the third harmonic components of rotor magnetic fields, this brushless harmonic excitation principle is realized by injecting the third harmonic current component or high frequency single-phase current component or DC component into the three phase stator open windings, to generate a time pulsating magnetic field which can induce back-EMFs in the specially designed rotor harmonic coils. Through rectification, the induced back-EMFs are used to supply DC current to the rotor excitation winding. To verify the above principle, magnetic field calculations and prototyping tests were carried on. The significance of this harmonic excitation principle is to provide a new brushless machine option to reduce the consumption of increasingly expensive rare earth permanent magnetic material by machines in some applications.