2-D Analytical Model for External Rotor Brushless PM Machines

This paper presents a 2-dimensional analytical model for external rotor brushless machines with surface mounted magnets. The subdomain technique is used to divide the problem into magnets, airgap, slot-openings, and slots regions. The magnetic flux density distributions are initially calculated, and then the important quantities of the machine such as back electromotive force, cogging torque, electromagnetic torque, self- and mutual-inductances, and unbalanced magnetic forces are computed. The finite-element method and experimental results are used to confirm the validity of the proposed model.