Development of a Linear Vernier Hybrid Machine for direct drive wave energy converters

Abstract

The work presented in this thesis concerns the development of linear electric machines for use with wave energy converters. The machine topology selected, the Linear Vernier Hybrid Machine, is extensively investigated, specifically looking at alternative magnet configurations. Topologies are evaluated by their generation capabilities at low velocities, as demanded by Direct Drive Wave Energy Converters. Attention is mainly focused on improving the electromagnetic performance and reducing the magnet mass. A new topology of the Linear Vernier Hybrid Machine is proposed for these purposes, known later as Inset Magnet Consequent Pole machine. Tapered ferromagnetic poles are employed in this topology, which have shown a great impact on minimising the inherent pole-to-pole leakage flux as well as the unwanted cogging force. Further investigation into the Inset Magnet Consequent Pole machine focuses on improving the power factor through modifications made to the machine structure with no increase in the mass magnet, steel or copper used. Two novel variants with the added benefit of flux concentration effect are proposed and described. Finite Element Analysis is used to optimize, analyse and compare the electromagnetic performances for the three investigated machines. Considering the complexity of manufacturing and number of components, two selected topologies are built and tested in the laboratory, the Inset Magnet Consequent Pole machine and V-shape Consequent Pole machine. The experimental results are compared to the simulation results to validate the design. In general, a good agreement is shown between the predicted and measured results. Afterwards, the experimental results obtained from the two prototypes are compared with each other. These results verify that the proposed V-shape Consequent Pole topology is superior in terms of no-load back EMF, force and power factor, while it exhibits lower cogging force in comparison with the Inset Magnet Consequent Pole topology. It is therefore concluded that the V-shape Consequent Pole machine is the best compromise between power factor, efficiency and ease of manufacture. It has half the number of components per pole of the best machine design presented, yet delivers 91% of the force density and 93% of the power factor. The last part of this thesis investigates the feasibility of using the proposed V-shape Consequent Pole machine as an alternative design for an existing wave energy device developed by Uppsala University to assess the effect of employing this sort of machine on Abstract ii the overall machine size and costs. Five variants of the V-shape Consequent Pole machine are described and compared