Analytical calculation of open-circuit magnetic field distribution of slotless brushless PM machines

A comprehensive analytical open-circuit magnetic field distribution of slotless brushless permanent magnet machines with surface mounted magnets is presented for six different magnetization patterns. The stator and rotor back-irons are assumed to be finite permeable. Therefore, the analytical model covers five annular regions: rotor; magnet; air–gap/winding; stator; and exterior. The expressions of the five regions are presented in a convenient form to ease the numerical computation for both internal and external rotor motors. The induced back-EMF is also expressed analytically. The efficacy of the analytical model is validated by comparing the results with finite element analyses (FEAs).

► Analytical magnetic field distribution of permanent magnet brushless machines. ► Analytical expression of the back electromotive force (EMF). ► A comparative study on the effects of different magnetization patterns on the magnetic flux density and back-EMF. ► Evaluate the performance of the analytical study with the finite element method.