Design, analysis and application of direct-drive permanent magnet linear machines

Abstract

For practical application of the transportation and factory automation system, the distinct advantage of the linear machine is the omission of the linear-to-rotary transmission mechanism. In recent years, linear permanent magnet (PM) machines are becoming more and more attractive due to the significant development of PM materials and the huge achievements of power electronic devices. A general overview on the development of linear machines, the advanced dual-PM machines and some practical applications of the linear machines are presented. Furthermore, the research objectives and brief introduction of each chapter are given. First, a new PM linear magnetic-geared machine is proposed for the application of the free-piston generator in the series hybrid electric vehicles (HEVs). By integrating the linear magnetic gear and linear permanent magnet synchronous machine together, the proposed magnetic-geared machine is obtained. This work is analyzed and verified with the help of the finite element analysis (FEA) method. It proves that the proposed magnetic-geared machine has higher efficiency, higher power density and lower weight than the conventional linear machines together with the magnetic gears. Second, the double-sided long-stator type permanent magnet linear machines (PMLMs) for the ropeless elevator system are studied. Design considerations and criteria are given in detail. Then a comparative study is conducted on three PMLM configurations. The thrust forces, detent forces, no-load EMFs and translator mass are separately investigated by using the FEA simulations. The quantitative comparison results from FEA are concluded. Third, a study on a new kind of machine for the application of regenerative shock absorbers. By incorporating the stator-PM structure and mover-PM structure into one doubly salient PM (DSPM) machine topology, leading to a new class of machine called the doubly salient dual-PM (DSDPM) linear machine. For the DSPM machine, all PMs are firstly mounted on both the stator and mover iron, hence offering the high force density, high power density and high efficiency without changing the machine size. The topology and performances of the proposed machine are presented, and an optimal design is performed, which verifies the advantages and validity of the designed machine. The results show that the proposed BF-DSPM machine not only retains the advantages of the conventional linear DSPM machine, but also improves the force density, power density and efficiency compared with the existing ones. Last, the study focuses on a comparison of five dual-PM linear motors, which can be the potential candidates for the ropeless elevator system. Since the PMs are put on both the stator and mover of the proposed linear motors, the dual-PM linear motors are obtained. By analyzing the electromagnetic performances, five dual-PM machines are quantitatively compared. In summary, the double-mover tooth-PM linear machine is favorable to the application of ropeless elevator propulsion system, resulting from its small attraction force, low force ripple and high force density. In the end, the experimental verifications are performed to verify the study.