Abstract: In order to solve the defects that mass computer resource and time for parametric design or optimization in finite element method (FEM) are wasted, based on the analysis method which combined magnetic field with magnetic circuit, a concise and efficient analytical approach is put forward for the calculation of the air-gap magnetic field and torque of modulated permanent magnetic gear. Without ferromagnetic pole-pieces, a magnetic field formula is induced for the air-gap that adjacent to high speed permanent magnetic ring, according to the magnetic scalar potential theory in the static magnetic field; by the equivalent magnetic circuit methods, the ferromagnetic pole-pieces is expressed as air-gap permeance function to improve the formula; magnets of the low speed permanent magnetic ring are reduced to a distribution of equivalent current, which experiences the Lorentz force in external magnetic field for torque calculation. As the calculating results, the formula is accurate but faster than the FEM. The mathematics model is suited for programmable calculation and that will make the structural and parametric design or optimization of modulated permanent magnetic gear simple and time saving.

Key words: Air-gap magnetic field, Magnetic field modulated, Permanent magnetic gear, Torque