Optimization and comparison of linear transverse flux and flux switching machines

Abstract

This paper investigates the design of alternative permanent magnet linear machines for use as the generator in a free piston engine. All of the machines are of a modulated pole structure with three dimensional flux flows. In transverse flux machines such as these, the current flows in a different plane to the flux path, eliminating the usual conflict between electric and magnetic loading. For a linear machine, the mass of magnets used is sensitive to whether the magnets are mounted on the stator or translator. Hence this paper compares transverse flux machines with translator mounted magnets and flux switching machines with stator mounted magnets. A three dimensional finite element analysis of each topology is run through an optimization routine in order to investigate the magnet usage, power factor and other performance criteria. It is concluded that flux switching machine is uncompetitive due to the 65% flux leakage even with improved tooth structure, moreover the transverse flux machine is shown to perform better overall, giving a better power factor, better efficiency and lower translator mass as a whole flux switching machine is not match for free piston engine applications.

Study of the assembly, build and test of a linear transverse flux machine

“…The initial machine topology based on previous studies [9] is shown in Fig. 1, where the translator has axially magnetised permanent magnets separated by iron pole pieces, the stator consists of three separate phases, each with a set of iron teeth surrounding the copper coil.…”

“…In previous studies [7–9], linear TFMs have been compared with more conventional longitudinal topologies for use with a free‐piston engine. Simulation results show that a modulated pole machine (MPM)‐type TFM topology can achieve high force, low copper loss, and competitive power factor even under conditions of high electric loading.…”

A Review of the Design and Control of Free-Piston Linear Generator

“…The flux leakage analysis of the TFPMLEMs pointed out that reduction of the armature flux leakage can increase the power factor, and different stator topologies are investigated [16,30]. During the design process, a three dimensional (3D) finite element analysis (FEA) is necessary due to the complex geometry and fully 3D flux path [31]. The mover of FSPMLEM is made of slotted iron, the stator consists of PMs and transverse windings for each phase, as shown in Figure 4 [31].…”

“…As a result, FSPMLEMs have superior reliability due to their simple and rugged mover structure, and they are featured with high force density, high efficiency but high force ripple [32,33]. The mover of FSPMLEM is made of slotted iron, the stator consists of PMs and transverse windings for each phase, as shown in Figure 4 [31]. As a result, FSPMLEMs have superior reliability due to their simple and rugged mover structure, and they are featured with high force density, high efficiency but high force ripple [32,33].…”

“…And numerical optimization results of 3D FEA concluded that the FSPMLEMs were uncompetitive compared to the TFPMLEMs due to the large flux leakage even with improved tooth structure. However, complex structure and low power factor for TFPMLEMs remain to be solved [23,31,34]. Compared to SMPMLEMs, both of them suffered from a large moving mass which would result in low motion frequency and low dynamic response.…”