Minimization of detent force in a 1 kW linear permanent magnet generator for the conversion of sea waves energy: Numerical and experimental validation

Linear permanent magnet generators are widely considered for the direct conversion of energy contained in sea waves. Both planar and tubular structures have been proposed and all these structures present several advantages: relative high efficiency, simplicity of the structures, high sturdiness. However, as all other linear machines they present some drawbacks: oscillations in the movement, distortion in the generated electromotive force (emf), etc. In this paper we focus our attention on the parasitic oscillations of the translator which are caused by the presence of a high detent force. Detent force is generated by the fact that magnetic energy presents a minimum when the length of the magnetic flux lines reaches a minimum. Detent force can reach high values and can reduce the quality of emf generated and the reliability of the machine. Thanks to a 3D FEM simulator, we have studied its behavior in a multiphysics approach and we have studied several possible designs. For the sake of the simplicity of this digest, we skip the details of the preliminary sizing of the generator, that essentially consisted in the maximization of the force that can be experienced by the translator at maximum electrical loading for the maximum sea wave speed.