Minimization of Cogging Force in Fractional-Slot Permanent Magnet Linear Motors with Double-Layer Concentrated Windings

Abstract

Permanent magnet linear motors (PMLMs) with double-layer concentrated windings generally show significant cogging forces due to the introduction of auxiliary teeth for eliminating the end-effect induced phase unbalance, even when the fractional-slot technology is applied. This paper presents a novel approach to reduce the cogging force by adjusting the armature core dimensions in fractional-slot PMLMs with double-layer concentrated windings, together with magnet skewing. It is shown that the proposed technique is capable of reducing the cogging force of the motor in an effective way, with the peak value minimized to less than 0.4% of the rated thrust force in the case study. Such a technique can also be applicable to other linear motors with appropriate changes.

A system capable of dampening roll and producing electricity installed on the hull of a fishing vessel

“…In perfect analogy, given the different motion, in linear machines the mobile part is called the translator, while the fixed part retains the name of stator. Given the different nature of motion, the driving or braking torque typical of rotating machines is replaced by the driving or braking force of linear machines [24].…”

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“…To analytically approach the analysis, several methodologies are presented in [9,10,14]. In this case, a simplified magnetic equivalent circuit based on Figure 1 is proposed (see Figure 5).…”

“…Different techniques have been proposed for the reduction in detent force, the most usual are aside PM skewing and PM length/width adjustment [4,5], an asymmetric arrangement of PM, use of semi-closed slots [6], and utilization of auxiliary teeth or teeth notching [7]. Some other techniques use specific control strategies [8], in some cases, a combination of control and Energies 2020, 13, 5162 2 of 16 structural design (e.g., skewing PM, Halbach array) are employed [9,10], and others are based on the shift of the permanent magnets, poles and slots, the slots or poles and the distance between the magnet segments of each pole [11][12][13][14].…”

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“…In a similar way, the alternance of teeth and slots produces also a cogging force in linear machines [49]. In addition, linear machines are also affected by the "end effect" in the generation of the cogging force [50]. Indeed, in rotary machines, all permanent magnets are located inside the stator regions, whereas in linear machines, it is possible that magnets are forced to enter and exit the region delimited by the stator, especially if the long translator configuration is adopted.…”

“…Therefore, solutions normally proposed in rotary machines solve only a part of the problem pertaining to the cogging force in case of linear machines [52]. To solve the end effect, specific solutions should be adopted, like the optimization of the shape of the auxiliary teeth (the first one and the last one) in the stator, in order to minimize this phenomenon [50].…”