Alternative Configurations of VHM

With confidence in the FEA, the design tools presented here can be extended to consider larger machines. It is likely that manufacturing constraints may prevent the use of airgaps as tight as 1 mm. Expansion of the airgap, say to 5 mm, has several effects. The shear stress and attractive forces are both reduced and the optimum magnet width, as calculated by (4.6) and shown in Figure 4.4, increases.

The configuration used throughout this Chapter has meant that the useful flux links all four coils in a phase, passing straight through the translator back iron. By altering the polarity of the magnets and the interconnection of the coils, it is possible to shift the flux pattern so that the flux linking the two stator cores are totally independent, having a return path through the centre of the rotor, Figure 4.68.

Figure 4.68: Alternative flux pattern

Electrically, this will have no effect on the machine, but several physical effects will become apparent. In this configuration, as all the flux no longer follows the same reluctance path, any deviation of the translator position towards one or other stator core will cause an imbalance in the coil driven-flux density in the two airgaps. The unfortunate side effect of this is a sharp increase in the resultant force on the translator, referring to Figure 4.19 the attraction to one side will move up the curves whilst the attraction to the other moves down. In the original flux pattern, the coil driven flux will be equal on either side of an unevenly spaced translator, and the unbalanced forces will be limited to those due to magnet excitation, the lowest curve of Figure 4.19.

If the return flux path is through the translator, a large back iron will be required and the structure will necessarily be large. However, a significant advantage of having a translator return flux path is that it allows for the possibility of a four sided electrical machine, all being magnetically independent. Figure 4.69 shows an end view of the configuration, with the translator oscillation into and out of the plain of paper.

Figure 4.69: End view of four sided VHM

The resulting machine can be much shorter in the axial direction than a two sided machine having the same active airgap. This topology, which has an aspect ratio closer to that of a hydraulic ram, is further discussed in Chapter 7.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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