A Fast Method for Calculating the Air-Gap Flux and Electromagnetic Force Distribution in Surface Permanent Magnet Motors

This paper proposes a new method for calculating the air-gap flux and electromagnetic (EM) force distribution induced by PWM current harmonics in inverter-fed surface permanent magnet motors. First, the concept of permeance distribution function (PDF) is introduced to calculate the air-gap flux distribution excited by armature currents of the motor. Then, the air-gap flux distribution excited by permanent magnets is calculated using the relative permeance method. The actual air-gap flux distribution is consequently obtained by the superposition principle. Using the Maxwell stress tensor method, the radial EM force distribution on the motor air gap can be obtained. Finally, the calculated EM force distribution is evaluated by 2-D FFT and validated against finite element analysis, demonstrating good accuracy and very fast computation time.