On-Load Cogging Torque Calculation in Surface-Mounted Permanent Magnet Motors Using Hybrid Analytical Model

This article presents a new hybrid analytical model (HAM) based on sub-domain (S-D) model for surface-mounted permanent magnet (SMPM) synchronous motors, which helps from magnetic equivalent circuit (MEC) model to calculate the cogging torque (CT) under loading condition. For this purpose, the conformal mapping (CM) method and Hague solution are used to calculate the air-gap permeances, which are to be employed in MEC model for calculating the distribution of magnetomotive force (MMF) drops in iron parts of stator for every operating point. The distribution of MMF drops is then translated into the distribution of equivalent virtual currents in stator slots of SMPM motor for relevant operating point. While considering the permanent magnets (PMs) on the surface of rotor core and the virtual currents in the stator slots, S-D model is used to calculate the components of air-gap magnetic field under loaded condition. Maxwell stress tensor (MST) method is then used to calculate the CT under loaded condition. In final, the frozen permeability method (FPM) is used to verify the analytical results obtained through HAM.