A Novel Analysis Method for Flatted Single-Layer Interior Permanent Magnet Machines Having Overhang Structure

This study describes a novel analysis method for interior permanent magnet (IPM) machines with an overhang, in which the rotor axial length exceeds that of the stator. Adopting an overhang structure facilitates the achievement of a high torque density per machine volume without increasing the stator size due to the additional magnetic flux of the rotor. However, the use of the three-dimensional (3-D) finite-element method (FEM) is inevitable, which requires substantial computation time and large computer memory to accommodate the overhang effect. Therefore, a new analysis method combined with a lumped magnetic equivalent circuit (MEC) is proposed to overcome the inefficient conventional approach. A new residual flux density can be derived by considering the magnetic flux paths in the overhang structure. Two-dimensional FEM combined with the residual accurately considers the IPM with overhang. The validity of the proposed concept is verified via 3-D FEM using several test models.