Analysis and Optimization of Ironless Permanent-Magnet Linear Motor for Improving Thrust

Abstract

As known, improving launcher thrust is the goal that the mankind is pursuing. There is no saturation phenomenon in the ironless permanent-magnet linear motor (IPMLM); hence, the thrust of IPMLM has a linear relationship with current through windings to provide larger thrust. The topology of IPMLM determines that its thrust fluctuation is smaller than that of an iron permanent-magnet linear motor. In this paper, the model of an air-gap magnetic field is established by the magnetic charge model and the image method for global optimization of IPMLM thrust. All dimensions of IPMLM are described by motor thickness and three ratio coefficients (i.e., α, β , and γ). The cooling power of the cooling system under different temperature gradients, which determines current density of winding, is calculated by Comsol software. Different values of α, β, and γ mean that each dimension of IPMLM is different, the current density in different windings being subject to constraint condition <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cu</sub> ≤ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> . Therefore, we can obtain the variation of current density with dimension and the variation of thrust with dimension. For obtaining maximum thrust in the same volume, the size ratio among magnetic structure, winding structure, and cooling structure is derived by the thrust analytical expression. The distribution of the IPMLM thermal field is analyzed by a 3-D finite-element method, and this optimization method of IPMLM thrust density is proved by experiment.