Abstract
A single-phase tubular permanent-magnet linear machine (PMLM) with hybrid Halbach/axially-magnetized PM arrays is proposed for free-piston Stirling power generation system. Machine topology and operating principle are elaborately illustrated. With the sinusoidal speed characteristic of the free-piston Stirling engine considered, the proposed machine is designed and calculated by finite-element analysis (FEA). The main structural parameters, such as outer radius of the mover, radial length of both the axially-magnetized PMs and ferromagnetic poles, axial length of both the middle and end radially-magnetized PMs, etc., are optimized to improve both the force capability and power density. Compared with the conventional PMLMs, the proposed machine features high mass and volume power density, and has the advantages of simple control and low converter cost. The proposed machine topology is applicable to tubular PMLMs with any phases.
Highlights
Free-piston Stirling power generation system, which integrates a free-piston Stirling engine with a tubular linear machine, is increasingly investigated for applications where require quiet operation, high reliability and long service life.[1,2] Owing to the advantages of high power density and high efficiency, permanent-magnet linear machines (PMLMs) are inherently suitable for the Stirling generation system.[3,4] There are three kinds of mover topologies for conventional tubular PMLMs, i.e., movers with radially, axially, and Halbach magnetized permanent magnets (PMs).[5,6] Structure of the radially-magnetized PM mover is relatively simple, but it needs thick mover core, which leads to large mover mass
The radially-magnetized PM rings are inset in the bore of the ferromagnetic poles, and the axially-magnetized PMs are sandwiched between the ferromagnetic poles
Since the mover of the proposed machine can be considered as an axiallymagnetized PM mover whose bore embeds a Halbach array, the proposed machine is named as hybrid Halbach/axially-magnetized PMLM
Summary
Free-piston Stirling power generation system, which integrates a free-piston Stirling engine with a tubular linear machine, is increasingly investigated for applications where require quiet operation, high reliability and long service life.[1,2] Owing to the advantages of high power density and high efficiency, permanent-magnet linear machines (PMLMs) are inherently suitable for the Stirling generation system.[3,4] There are three kinds of mover topologies for conventional tubular PMLMs, i.e., movers with radially-, axially-, and Halbach magnetized permanent magnets (PMs).[5,6] Structure of the radially-magnetized PM mover is relatively simple, but it needs thick mover core, which leads to large mover mass. While the homopolar radially-magnetized PM ring is difficult to manufacture, so the homopolar PM ring is generally assembled by several cambered PM segments in the manufacturing process, and these PM segments are banded by fabric bandages, which increases the equivalent air-gap length and compromises the machine performance.[8,9]. We propose a single-phase tubular PMLM with hybrid Halbach/axially-magnetized PMs. The proposed machine has the advantages of both the axially-magnetized and Halbach PMLMs, such as high air-gap flux density. The proposed machine has the advantages of both the axially-magnetized and Halbach PMLMs, such as high air-gap flux density It eliminates the leakage flux problem inside the axially-magnetized PMLM and solves the fixation problem of the cambered radially-magnetized PM segments in the Halbach PMLM.
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