On Torque Improvement by Current Harmonic Injection in Isotropic and Anisotropic Multiphase Machines

Multiphase machines give the possibility to increase the torque injecting and controlling current harmonics of different orders. This work investigates the current harmonic injection techniques for both isotropic and anisotropic machines. The proposed analysis shows that for anisotropic machines, both amplitudes and angles of the optimal current injection should not be predicted based on the back electromotive force only. An analytical model is used to assess the differences in terms of no load and load voltage spectra. Considering these differences, a current injection technique based on the harmonic content of the voltage waveforms is proposed. In addition, the analysis to determine the optimum amplitudes and angles to maximize the torque capability is carried out by means of finite-element analysis (FEA) and compared with the techniques based on the analytical model. The FEA is carried out for both surface permanent magnet and V-shaped interior permanent magnet (IPM) machines with dual-three-phase winding layouts and injecting the fifth harmonic of current. Finally, the proposed concept is validated via an experimental test on a dual-three-phase V-shaped IPM machine. The results show that current harmonic injection based on the voltage vectors is applicable for both isotropic and anisotropic machines with good accuracy.