Harmonic Model of a Nine-Phase Synchronous Machine in Healthy and Faulty Conditions

This thesis presents a harmonic model of a nine-phase permanent magnet synchronous machine (PMSM) in healthy and faulty conditions. The motivation for using a nine-phase PMSM is its inherent fault-tolerant capability and the possibility of enhancing the torque production by stator current harmonic injection. The machine model, the connection and winding arrangements, and the spatial harmonics analysis are described. The open-circuit (OC) faults and their effects on the machine performance are discussed. A vector space decomposition (VSD) transform is employed to decouple the machine model into orthogonal subspaces corresponding to different space harmonics. Three types of VSD transforms available in the literature are compared. An advanced control scheme based on n-dim VSD derived from a multimachine multiconverter model is proposed. This innovative approach treats the nine-phase machine as four separate fictitious machines using Concordia-type orthonormal transformations to simplify complex voltage equations. Assumptions of no saturation or eddy currents ensure optimal performance with PI current controllers in steady state. A control strategy based on odd current harmonic injections up to order seven is proposed to achieve improved torque performance in case of OC or double phase OC faults. The key details and the advantages of the proposed strategy are highlighted. The results of the harmonic model and the control strategy are validated by simulations and experiments