Electromagnetic Design of a 10-kW-Class Flux-Switching Linear Superconducting Hybrid Excitation Generator for Wave Energy Conversion

Research on linear generators for direct-drive wave energy conversion has mostly focused on inner-secondary sole permanent magnet (PM) linear generators, among which vernier hybrid machine and flux-switching generators are considered as the best selection. In this study, an outer-secondary tubular superconducting hybrid excitation linear generator is presented to increase the power density and reduce the voltage regulation. Double-buoys direct-drive WEC is introduced. The operation under hybrid excitation is analyzed. With consideration to cogging force, the linear generator is optimized. The generator performance is evaluated using the finite element method. Based on the on-load performance, a hybrid excitation method is proposed and is compared with only the PM working. According to the working point of the proposed generator, losses of the superconducting hybrid excitation windings are calculated. A PM flux-switching generator is employed to verify the analysis results. The results show that the proposed generator has the advantages of larger air-gap effective area, higher power density, and more steady output power and voltage.