A Yokeless Linear Permanent Magnet Machine

This paper presents a novel yokeless linear permanent magnet (PM) machine topology. The armature windings employ fractional slot concentric configuration and can be prewound on separate teeth consecutively or alternatively with a high slot filling factor. A number of advantages are obtained from the proposed yokeless topology. First, the volume of the iron core is reduced and more space is available for the windings, which leads to higher force density, lower copper loss, and higher efficiency. The absence of the yoke iron also reduces the iron loss and like-hood of saturation, and hence improves efficiency and linearity of thrust force characteristic. Without the yoke, the slot leakage flux and the magnetomotive force drop in the iron core are also reduced and consequently the utilization of PMs and the machine force capability are improved. These benefits are demonstrated through a design case study.