Induced voltage harmonic reduction of PM cylindrical machines

Typically, permanent magnet (PM) machines with surface-mounted magnets have trapezoidal induced voltage waveforms with high harmonic content that can adversely affect torque pulsations, noise, and efficiency. A simple methodology for reducing these harmonics by selecting the appropriate magnet shape and dimensions has been introduced previously by the authors (see IEEE Proc. PES 1989 Summer Mtg.). For illustrative purposes, however, the method used a simplified analytical model of the magnetic circuit, ignoring important factors such as curvature and magnet leakage. The authors presently apply the proposed methodology to cylindrical machines using a more precise model. The results, showing the potential for reducing induced-voltage harmonics by using a double-magnet per pole configuration, have been verified by comparison with results obtained from finite element analysis.>