Modeling of a Permanent Magnet Linear Generator for Wave-Energy Conversion

This paper begins with a brief review of the equation of motion for a generic floating body with modification to incorporate the influence of a power-take-off (PTO) unit. Since the damping coefficient is considered the dominant contribution to the PTO reaction force, the optimum non time-varying values are presented for all frequencies, recovering the well-known impedance-matching principle at the resonance condition of the coupled system. The construction of a laboratory-scale permanent magnet linear generator (PMLG), developed at the University of California at Berkeley, is discussed along with the basic electromagnetic equations used to model its performance. Modeling of the PMLG begins with a lumped magnetic circuit analysis, which provides an analytical solution to predict the magnetic flux available for power conversion. The voltage generated across each phase of the stator, induced by the motion of the armature, provides an estimate for the electromagnetic damping as a function of the applied resistive load. The performance of the PMLG and the validation of the proposed analytical model is completed by a set of dry-bench tests. Results from the bench test showed good agreement with the described electromechanical model, thus providing an analytical solution that can assist in further optimization of the PMLG.