Analysis of Cogging Torque and its Effect on Direct Torque Control (DTC) in a Segmented Interior Permanent Magnet Machine

This paper investigates reduced cogging torque seen in the Segmented Interior Permanent Magnet (SIPM) machine and explores the effects of cogging torque on direct torque control (DTC) performance. In the segmented IPM machine, the pole magnets are segmented to provide an improved flux-weakening capability to the rotor. The cogging torque of the segmented IPM machine is found to be significantly lower than that of a conventional, non-segmented IPM machine of similar ratings and dimensions. The cogging torque of the segmented IPM machine was first calculated using finite element analysis which was verified later by experimental measurements. The cogging torque of the conventional IPM rotor, using the same stator, was also calculated and measured. The DTC was implemented on both the segmented and conventional IPM machines to observe the effects of cogging torque on the speed, torque and flux performance of the controller. This paper presents results of cogging torque comparison and its effects on DTC performance between the two machines, and a detailed analysis of the reduced cogging torque seen in the Segmented IPM machine.