Design, analysis and application of low-speed permanent magnet linear machines

Abstract

With the growing interests and high requirements in low-speed linear drives, the linear machines possessing high force density, high power density and high efficiency feature become in great demands for the linear direct-drive applications. There are many available linear machine topologies, but their performances for exhibiting the high-force density capability dissatisfy the industrial requirements. In order to solve this problem, the new machine topologies emphasizing on high force density are explored and studied. The objective of this thesis is to present the design, analysis, and application of permanent magnet (PM) linear machines which can offer a higher force density at the same magnetic loading and electric loading than the conventional machines.

Although in recent years there are many emerging advanced PM rotational machines for direct-drive rotational drives, the development of advanced PM linear machines for direct-drive linear drives is sparse. In spite of the motion type of electric machines, the inherent operating principle is the same. By studying and borrowing concepts of the high torque density rotational electric machines, the linear machine morphologies of the promising candidates are designed and analyzed. The problems and side effects resulting from the linearization are discussed and suppressed.

Two main approaches for machine design and analysis are developed and applied, namely the analytical calculation and the finite element method (FEM). By analytically solving the magnetic field problem, the relationships between the field quantities and the machine geometry are unveiled. With the use of analytical calculation, the machine design and dimension optimization are conveniently achieved. With the use of FEM, the machine design objective and its electromagnetic performance are verified and evaluated.

Finally, the proposed low-speed PM linear machine is applied for direct-drive wave power generation. By mathematically modeling the wave power, generation system and the generator, the conditions for maximum power harvesting are determined. By using the vector control, the generator output power is maximized which is verified by the simulation results.