Prediction of No-Load Flux Density Distribution in Permanent Magnet Machines

Both the average output torque as well as the output torque pulsations of permanent magnet (PM) motors depend on the air gap flux density waveform produced by the magnets. An analytical model is presented, which uses the two-dimensional field theory in polar coordinates to determine the flux density waveforms at the stator and rotor surfaces of PM machines and also the amount of magnetic flux entering these surfaces. The analysis is valid for dc as well as for synchronous brushless motors with magnets which are magnetized in either the radial or the parallel direction. The results obtained by the model are verified by comparison with results obtained by finite-element analysis as well as with test results.