Transformation Calculation Between the Inner and Outer Rotor Permanent Magnet Motors

In this paper, an equivalent conversion method for inner-rotor and outer-rotor permanent magnet motors that considers curvature effects is proposed. To consider the flux focusing and flux diffusion effects of different rotor structures, the transformation theory is derived in detail with the center radius of the air gap as the transformation reference. In addition, according to the harmonic modeling (HM) technology, a nonlinear semi-analytical model of a surface-mounted inner-rotor motor is established, and the proposed conversion method is verified. The finite element method (FEM) and experimental results are in good agreement with the results of the proposed method. Using the equivalent transformation theory, engineers can use an existing mature surface-mounted inner-rotor permanent magnet motor to design, simulate, and evaluate a surface-mounted outer-rotor permanent magnet motor, and vice versa.