Cogging torque reduction in interior permanent magnet brushless dc motor with flux-concentration type rotor

An improved pole arc combination method to minimize the cogging torque in the interior permanent magnet brushless dc motor with flux-concentration type rotor is presented. Due to the magnetic saturation and relative complex structure, the cogging torque in interior permanent magnet brushless machines is more complicated than that in the surface permanent magnet brushless machines. Pole arc combination method offers a better alternative for cogging torque reduction in the interior permanent magnet brushless machines from the point of view of cost and convenience. Based on the mathematical analysis of the resultant cogging torque, the relationship between the pole arc widths for combination is found. To overcome the drawback of the existing pole arc combination method, an improved method is presented. Using the finite element method and a comparison program, the optimal pole arc widths for combination are searched out, and considerable reduction of the cogging torque is obtained. Superposition technique is adopted to validate the feasibility of the proposed method.