This paper discusses the development of linear Vernier Hybrid Machines for use in wave energy converters. A number of topology options are explored to reduce magnet usage and improve performance for use as a linear generator. Consequent pole, V-shape and Halbach arrays are designed for a target 25kW specification. A discussion of overall cost of energy produced is used to justify using efficiency and power factor to asses fixed magnet mass topology variants. A power factor improvement from 0.38 to 0.72 is presented. Physical integration of the electrical machine into wave energy converters is considered including flooded experimental results of thermal behavior and polymer bearing wear.

Air-cored machines offer benefits in terms the elimination of magnetic attraction forces between stator and rotor. With no iron in the stator there is not a good thermal conduction path for heat generated by Joule losses in the stator winding. Results from both models and experimental tests are provided in this paper to investigate different methods of cooling air-cored windings, including natural air-cooling, direct liquid cooling and the use of heat pipes.

Demagnetization of permanent magnet machines is a fault that evolves over time leading to an eventual catastrophic failure. This condition is of particular interest in renewables, with emphasis on remote applications such as offshore wind, tidal and wave energy harvesting. Moreover, the demagnetization fault can be either uniform or non-uniform. The strong majority of research papers are focusing on non-uniform demagnetization and typically study the case of a single faulty magnet. This is because, the uniform demagnetization does not create harmonics that can be detected with spectral methods. Despite the above, the study of single magnet demagnetization studies have been criticized due to being unrealistic to describe most practical cases where permanent magnet machines are subjected to demagnetization due to overloading and/or overheating conditions and leading to uniform demagnetization. This paper sheds some light into such theories, while studying a, realistically induced in the lab, demagnetization case of a direct-drive C-GEN permanent magnet generator. The goals of this research are to examine the generated harmonic index due to the fault, the distribution of the demagnetization in space and the impact of the fault on the multiple generator stages due to the circulating currents.

Two different concepts of wave energy converter coupled to the novel C-GEN linear generator have been studied numerically, including the evaluation of different buoy sizes. The first concept has a slack connection between the buoy and the generator on the seabed. Another concept is based on a stiff connection between the buoy and the generator placed on an offshore platform. Three different approaches to calculate the damping force have been utilized within this study: the optimal damping coefficient, R-load, and $RC$-load. R-load is a model for the load applied to a grid-connected generator with passive rectification. $RC$-load is a model for a phase angle compensation applied to a system with active rectification. The radiation forces originating from the oscillatory motion of the buoy have been approximated using the transfer function in the frequency domain and the vector fitting algorithm. A comparison of the approximation methods is presented, and their accuracy has been evaluated. The advantage of the vector fitting method has been shown, especially for higher approximation orders which fit the transfer function with high accuracy. The study’s final results are shown in terms of the absorbed power for the sea states of March 2018 at Wave Hub, UK.

This paper details the design and testing of a novel transverse flux claw pole linear machine suitable for large superconducting generators. The machine utilises a modular claw pole transducer design with a stationary field winding which eliminates the need for cryogenic couplers and electrical brushes for a superconducting machine. The results from this prototype will enable a better understanding of the electromagnetic and mechanical structures before embarking on a more costly super-conducting design. The structure of the prototype supports a field winding and core; four pairs of claw poles with a stroke of 500 mm; three armature windings and core. Tests will be preformed to determine the deflection of the airgap, field core and armature core, the induced voltage in the armature coils, the forces acting on the structure and the flux density variation in the claw poles.

Tidal energy is one of the world's most predicable renewable energy sources and therefore holds great potential to be a valuable building block for the decarbonisation of electricity production. This paper focuses on a Venturi shaped duct structure (shroud) to accelerate the flow speed at a vertical axis tidal turbine utilising the low static pressure created at the exit of the shroud. This concept is known as a Davidson Hill Venturi (DHV) turbine. By constructing the nozzle and diffusor using hydrofoils, initial demonstrations indicate increased system efficiency. However, owing to the potential number of geometric and structural hydrofoil variations, only a general description of the location of the hydrofoils is provided in order to facilitate modelling while allowing for future geometric variations to be devised. The conducted investigations focus on the influence of the nozzle and diffusor sections as the main geometry variations, identifying the length component in the orthogonal direction as the dominant parameter. By modelling multiple combinations of these variables it is clear that higher fluid velocities result in larger forces which must be supported by the devices structure. Small adjustments to the reference geometries hydrofoil placement and spacing provided improvements to the fluid flow. Thus, taking the slight alteration to the geometry as this papers main outcome, a further in a 3D-simulation study, including turbine interaction and rotation, is to be completed to fully characterise the systems benefits. The insights gained from this work will allow a reduction in computational costs for the detailed optimisation and study into the adaption of the concept for a wide range of (environmental) boundary conditions.