Slotless surface permanent-magnet (SPM) machines are attractive for many applications where it is important to minimize the cogging torque and or the eddy-current losses due to slotting effects. The design of these machines is often approached through Finite Element Analysis (FEA) simulations interfaced to design optimization programs, leading to a significant computational burden. In this paper, a compact but accurate sizing equation is established linking machine maximum torque to the main design data. The sizing equation can be used for a fast first-attempt sizing of the machine with no need for FEA simulations and no need for complicated magnetic field solutions. The proposed sizing approach is based on an explicit fully-analytical expression of machine torque, which is validated by FEA simulations.
