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Primary permanent-magnet linear generators have an advantage of a simple secondary structure, which is suitable for the application of wave energy conversion. Based on vernier hybrid machines (VHMs), which are widely used for direct-drive wave energy converters, this paper proposes a tubular superconducting flux-switching linear generator (TSFSLG), which can effectively improve the performance of this kind of generators. Magnesium-diboride (MgB 2 )-type direct current superconducting windings are used in the generator to increase the magnetic energy and overcome the disadvantages of easily irreversible demagnetization of the VHMs and high-voltage regulation of a permanent-magnet flux-switching linear generator (PMFSLG). The alternating current superconducting windings are implemented to improve the efficiency. Based on the MgB 2 superconducting wire produced and measured in the laboratory, the superconducting windings structure used for the generator is designed. The coil-EMF vector is optimized, and the losses of superconducting windings are analyzed. In addition, by using the finite-element method, the no-load performances of the generator are analyzed and compared with the ones of a VHM and a PMFSLG. Finally, the on-load performance of the TSFSLG is obtained by finite-element analysis and compared with the VHM and the PMFSLG. The results validate that the proposed generator is more suitable for wave energy conversion than its counterparts.Index Terms-Finite-element method, linear flux-switching generator, superconducting winding, wave energy conversion.

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Offshore wind generation is an important trend of global wind power generation. To reduce the cost of energy of offshore wind generation, high-power direct-drive wind turbines are being pursued around the world. With the development of superconductors and related technologies, superconducting (SC) generator offers a possible technological approach to produce largescale direct-drive wind turbines with a modest cost. A design of a SC wind generator (SCWG) for offshore direct-drive wind turbines is presented in this paper. The proposed SCWG is an electricallyexcited synchronous generator with stationary field windings made of low temperature superconductor wires. The electromagnetic design considerations on SCWG are studied. The description on design of copper rotor and SC stator are presented. Several key design technologies including rotor cooling and supporting structure design, SC field winding design, and cryogenic refrigeration system for SC magnets are analyzed. The weight and cost of the proposed SCWG are estimated and compared with that of a permanent magnet wind generator (PMWG) design and several existing similar SCWG designs. It is found that the proposed SCWG is 46% lighter than the PMWG with the same specifications. Moreover, a rough estimation of material cost of the SCWG is carried out, and comparison analysis of cost is also performed.  Index Terms-Offshore wind generation; high power wind turbine; superconducting generator; weight reduction; low temperature superconductor

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