Cogging torques [electric machines]

This paper gives a brief insight into a program of work undertaken to predict cogging torques due to various interactions in electrical machines and actuators. Any unwanted torque variations with position, due to variations in air gap geometry, or reluctance in the iron circuit, have been regarded as cogging torques, irrespective of the speed of rotation, or the levels of excitation, and therefore include the effects of armature reaction. For cylindrical air gap machines, by using 2 part piece-wise linear approximations to the magnetising characteristic, (B:H), it is possible to make reasonable calculations of torque using simple algebraic calculations of the `solenoid torques´ under the pole tips, even when neglecting hinging. For other cases, field based calculations (e.g. finite element programs) are usually more cost-effective in making accurate predictions. It is of note that cogging torques can be much higher with armature reaction effects