Magnetic field and force output analysis of tubular linear machines with two structure topologies

Arrangement of permanent magnet (PM) poles and windings influences the magnetic field and force output of linear machines significantly. Various designs of PM linear machines have been proposed by researchers, either putting PM poles inside and coils outside, or vice versa. However, there is no systematic comparison of these two types of designs in literatures. The purpose of this study is to compare the magnetic field and force output of linear machines with different PM and winding structure topologies. Halbach array can not only produce high flux density, but also has self-shielding effect. So it is employed for the analysis. Tubular structure is used because it helps to reduce flux leakage and enhance the system output performance. The magnetic field distribution of tubular linear motors with internal and external PM poles are formulated with Bessel functions, and the force output is thus obtained from Lorenz force law. The analytical models of magnetic field and force output are then validated with numerical computations. By utilizing the verified analytical models, design optimization is conducted with penalty functions for the two machine structures. The magnetic field and force output performance are then compared. It shows that the machine structure with internal PM poles helps to generate high force output. The study in this paper can also be implemented for the design of rotary machines.