A Two-Dimensional Analysis Model of Cogging Torque in Homopolar Inductor Machines

Because three-dimensional (3-D) finite element (FE) models cannot realize the fast computation of the cogging torque in homopolar inductor machines (HIMs), a two-dimensional (2-D) analysis model is needed to simplify the calculation of the 3-D FE models. However, the cogging torque calculated by the existing 2-D model are not accurate. Therefore, this paper proposes a novel 2-D analysis model to predict the HIM cogging torque accurately and quickly. The structure of the 2-D analysis model is obtained by the structures of the 3-D FE models and spatial overlap method. Then, the cogging torque of the 3-D and 2-D models is calculated theoretically. The equivalent principle between the cogging torque of two models is analyzed. Finally, a design example of a 48-slot/4-pole (48S4P) permanent magnet (PM) HIM is presented, and the prototype is manufactured. The cogging torque in the prototype is simulated by the 3-D and 2-D models and measured by a test bench. The simulation and experimental results verify the effectiveness of the proposed 2-D analysis model.