Design of polyphase motors with PM excitation

Design guidelines are presented for synchronous motors with permanent magnet (PM) excitation. A general model is established and the dependence of the electric and magnetic loadings on the angle between the armature and field excitations is put in evidence. For this angle there exists an optimal value which yields maximum torque for maximum allowable flux density in the teeth. Another value yields the minimum volume for the permanent magnets. These values guide the selection of the operating point of the motor and its preliminary design. It is found that, when the pole pitch exceeds a certain value, the magnet requires more space than a current carrying winding.