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Abstract
Linear flux switching permanent magnetic (LFSPM) machines, with the armature windings and magnets both on the mover in addition to a robust stator, are a good choice for long stoke applications, however, a large cogging force is also inevitable due to the double salient structure, and will worsen the system performance. Skewing methods are always employed for the rotary machines to reduce the cogging torque, and the rotor step-skewed method is a low-cost approximation of regular skewing. The step skewed method can also be applied to the linear machines, namely, the stator step skewed. In this paper, three stator step skewed structures, which are a three-step skewed stator, a two-step skewed stator and an improved two-step skewed stator, are employed for the cogging force reduction of two types of LFSPM machines. The three structures are analyzed and compared with emphasize on the influence of the skewed displacement on the cogging force and the average thrust force. Based on finite element analysis (FEA), proper skewed displacements are selected according to maximum difference between the reduction ratio of the cogging force and the decrease ratio of the average thrust force, then, the corresponding results are compared, and finally, valuable conclusions are drawn according to the comparison. The comparison presented in this paper will be useful to the cogging force reduction of LFSPM machines in general.
Highlights
Linear electrical machines can directly drive linear motion without the need of any rotation to translation conversion equipment, such as gear boxes, chains, and screw couplings, they are widely used in various applications, from urban transit, manufacturing automation to direct-drive servo and other linear propulsion systems [1,2,3,4,5,6,7,8,9].The linear induction motors (LIM) have simple structure, low cost and high reliability when used in high speed industrial transportation [1]
The linear switched reluctance motors (LSRM) can be used as linear drives owing to several reasons, such as one side of the machine only has concentrated windings, while the other side is robust without any windings or permanent magnets (PM), low expected manufacturing expense and a good fault tolerance capability [4]
A staggered stator tooth structure is proposed for the C-core linear flux switching permanent magnet (LFSPM) machines [20,21], and this structure can effectively reduce the cogging force according to proper displacement design of the two stator parts
Summary
Linear electrical machines can directly drive linear motion without the need of any rotation to translation conversion equipment, such as gear boxes, chains, and screw couplings, they are widely used in various applications, from urban transit, manufacturing automation to direct-drive servo and other linear propulsion systems [1,2,3,4,5,6,7,8,9]. A staggered stator tooth structure is proposed for the C-core LFSPM machines [20,21], and this structure can effectively reduce the cogging force according to proper displacement design of the two stator parts This method can be essentially treated as an improved two-step skewed stator structure, and is useful for the conventional LFSPM machines. The skewing methods will reduce the thrust force or thrust force density, the selection of the skewed structure and corresponding skewed displacement should consider the cogging force and the average thrust force In this stator step-skewed structures—a three-step skewed stator, a two-step skewed stator and an improved two-step skewed stator—are analyzed and compared for the cogging reduction of a conventional LFSPM machine and a modular LFSPM machine.
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