Magnetic Circuit Generators for Wave Power Plants, ch. 4-5

4 Results for mixed magnets and different pole shoes

The results for the simulations in Ace contain the magnetic energy (Ws/m) summed up in the stator steel. Moreoverit is possible to generate figures showing the magnetic field flowing through the stator, for example. Firstly, in Section 4.1, the result of Simulation 1 is presented. The simulation experiment of Simulation 1 was to investigate the outcome as one of the ferrite permanent magnets was divided into two parts, one of type Y30 and one of type Y40. Secondly, in Section 4.2, the result of Simulation 2 is presented, where a different shape of the pole shoes was investigated. Thirdly, in Section 4.3, the result of Simulation 3 is presented. Simulation 3 was the combination of a divided magnet and a differently shaped and sized pole shoe. The results will be analyzed in the final sections of the report, in order to investigate whether it is possible to create a linear generator for wave power production with different types of ferrite permanent magnets and pole shoes, but with a similar amount of magnetic energy in the stator steel as a design with only Y40 and rectangular shaped pole shoes.

4.1 Results of Simulation 1, mixed ferrite permanent magnets

The result of Simulation 1 is that Case 1, where the magnet is only made of Y40, generates the highest magnetic energy in the stator steel, in accordance with the hypothesis stated in Section 3.1. Case 2b, where 25% of the magnet is of type Y30 and 75 % of Y40, generates the second highest magnetic energy in the stator steel. It is concluded that the magnetic energy in the stator steel is higher for the cases where Y40 is placed closer to the stator than Y30. The total magnetic energy in the stator for each case can be seen in Table 6.

Table 6. The total magnetic energy in the stator different cases of mixed magnets.

MagPowTable6h250

Moreover , the magnetic flux through the stator for Case 2b is shown in Figure 18. The magnetic field strength (T) can be determined by the colors of the field, where red indicates a higher magnetic field strength and blue indicates a lower magnetic field strength.

4.2 Results of Simulation 2, differently designed pole shoes

The results of Simulation 2 are shown in Table 7. It can be concluded that the highest magnetic energy in the stator steel was obtained for the pole shoe design T, which consisted of a T-shaped pole shoe with a length of 120 mm and a width of 15 mm.

Table 7. The different pole shoe designs generate different magnetic energy in the stator steel.

MagPowTable7h100

Moreover, the magnetic flux through the stator steel for the design T is shown in Figure 19.

4.3 Results of Simulation 3, different magnets and pole shoes

The results of Simulation 3 are shown in Table 8. It is concluded that the highest magnetic energy in the stator steel was generated in Investigation 5, that is, a divided magnet where 25% of the magnet is of type Y30 and 75 % of Y40 along with a pole shoe of T-shape and with a length of 96 mm. Moreover , it is concluded that the shorter pole shoes of the T-shape generate a higher magnetic energy in the stator steel than the 120 mm long pole shoes of T-shape. Figures 20 and 21 show the magnetic field lines through the generator for Investigation 1 and 2, respectively. Figure 22 shows the magnetic field for a shorter T-shaped pole shoe, which was used in Investigations 3–5.

Table 8. Magnetic energy in stator steel for divided magnets and T-shaped pole shoes of different lengths.

MagPowTable8h150

[Figures 18–22 not shown]

 

5 Analysis of mixed magnets and different pole shoes

It is possible to create a linear generator for wave power production using different types of ferrite permanent magnets and pole shoes, but with a similar amount of magnetic energy in the stator steel. This means that the stated hypothesis in Section 3.1 was correct and, in a wider perspective, that future wave power plants could contain different types of ferrites.

However, all results have been generated with a simulation tool and there are, most certainly, errors between the simulated linear generator and a future possible real linear generator with mixed magnets and different designed pole shoes. For example, the tolerances in a real linear generator have a great impact on the final magnetic energy, although no direct issues concerning tolerances were addressed by the simulations. Moreover, there are several programmatic issues that could lead to errors. For example, the size and the geometry generated in Ace might include errors, as well as the number of calculation points chosen for the FEM calculations. As mentioned in Section 3.2, the simulation tool has proven to give accurate results in previous work, which can be studied by the interested reader [19].

Firstly, the results from Simulation 1 were analyzedAs can be concluded from Table 6 in Section 4.1 (with some exceptions), the more Y40 there is in the magnetic circuit, the higher magnetic energy in the stator steel, in accordance with the theory and hypothesis. Moreover, it was concluded that the magnetic energy in the stator steel is higher as the ferrite permanent magnet of type Y40 is put closer to the stator steel than the ferrite permanent magnet of type Y30 (see Table 6).

Secondly, the results from Simulation 2 were analyzed. As can be concluded from Table 7 in Section 4.2, the magnetic energy in the stator steel increases as the shape of the pole shoe is changed from a rectangular shape to a T-shape, in accordance with the hypothesis stated in Section 3.1. Moreover , as can be seen in Figure 19, the flux through the coil is more evenly divided among the stator coil for the case with a T-shaped pole shoe than for a rectangular pole shoe.

Thirdly, the results from Simulation 3 were analyzed. By comparing the results from Simulation 3, stated in Table 8 in Section 4.3, with the results from Simulation 1, in Table 6 in Section 4.1, it can be concluded that the magnetic energy in the stator steel increases as the magnets are divided and a T-shaped pole shoe is used, instead of a rectangular pole shoe. Furthermore, it was concluded that as the pole shoe was shortened to a certain degree, the magnetic energy in the stator steel increased. For the case with a T-shaped pole shoe and a magnet with 25% Y30 and 75% Y40, the pole shoe should be (96 mm) 80% of its full length to generate a maximum magnetic energy in the different cases tested.