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Highlights: [•] We model direct drive permanent magnet linear generators for wave energy converters. [•] We review the magnetic forces and the electrical output power. [•] We suggest new optimised design for direct drive linear generator. [•] The optimisation aims reduction of forces parallel and normal to axis of motion. [•] The optimisation aims increase of the electrical power output. [ABSTRACT FROM AUTHOR]

Direct driven permanent magnet linear generators (PMLGs) are an alternative solution for wave energy converters (WECs). Generally, problems such as high magnetic attraction forces between the permanent magnets and the magnetic core are associated with direct driven PMLG. To eliminate the attraction, air-cored generators can be used. They do not contain any stainless steel in either the stator or the rotor and therefore there is no magnetic attraction between the moving and the stationary parts. In this study, a novel design of multi-phase air-cored PMLG is proposed. The main advantage of the generator is the reduction in the Lorentz forces acting on the bearings by addressing the force in the direction parallel to the motion axis and elimination of cogging forces. Additionally, in the study a new system bypassing inactive coils is proposed and simulated as part of the grid integration system. The system achieves implementation of a small number of elements connected in series with the coils and hence the thermal losses in the grid integration system are reduced. All simulations are made by means of finite-element (FE) software working simultaneously with Matlab/Simulink. [ABSTRACT FROM AUTHOR]