Precise Control of Flat-Topped Air-Gap Magnetic Field in a Five-Phase Induction Machine Powered by Third-Harmonic-Injected Sinusoidal Supply

The third-harmonic-injected sinusoidal supply (THISS) can help make an innovative breakthrough to improve the power density of multi-phase induction machines. However, the existing typical control approaches cannot guarantee the machine to precisely generate expected flat-topped air-gap magnetic field under all operating conditions, which restricts the popularization of THISS. This article first converts the control objective from generating flat-topped air-gap field to air-gap flux linkage alignment. In conventional approaches, the rotor leakage flux linkage is not fully considered, and subjective hypothesis are proposed, resulting in the misalignment between air-gap flux linkages components with different harmonic order. Based on avoidance of exposed flaws and correct theoretical derivation, this article focuses on the spatial distribution of air-gap field, and gives priority to the alignment of the air-gap flux linkage by means of harmonic air-gap field-oriented vector control. The required third-harmonic field can be calculated in real time through the fundamental field. Therefore, the flat-topped air-gap field is ensured by fundamental and harmonic current loops. Furthermore, the controllers in fundamental and harmonic current loops are decoupling with each other. The theoretical analysis and proposed control approach are validated by simulation and experimental results in a five-phase induction machine (FPIM) powered by THISS.