Optimal design procedure for an external rotor permanent-magnet machine

External rotor machine design analytical algorithm is presented in this paper to calculate the main dimensions of the stator and rotor lamination. This procedure is based on the well known Lagrange multiplier method, where the airgap apparent power is maximized under tangential stress constraint Results of this procedure are used to generate an improved torque estimation algorithm based on the non-ideal structure of the machine. Finite element analysis is used to compare these results, establishing a good agreement with the analytical approach.