A new type of harmonic current excited brushless synchronous machine based on an open winding pattern

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, theoretical analysis, magnetic field calculations by FEA and experiments were carried out. The significance of this harmonic excitation principle is to provide a new brushless machine option in place of increasingly expensive permanent magnet machines in some applications.