Design and Analysis of 15 MW SPM Vernier Generator for Direct-Drive Wind Turbine Applications

Abstract

This paper presents the design and an analysis of a surface PM vernier generator (SPMVG) for MW-scale direct-drive (DD) wind turbine application. An SPMVG has the advantage of higher torque density; however, especially at higher power ratings with increased electrical loadings, the power factor worsens and there are some serious concerns including magnetic saturation of cores and PM demagnetization. These issues are directly related to machine design parameters such as PM dimensions, applied electrical loading, slot geometry and the choice of slot–pole combination. It is determined that depending on the PM thickness and a few other design variables, each slot–pole combination has an optimal value of specific electrical loading. The use of the optimal value of specific electrical loading ensures that the machine is not saturated, the performance is optimum and the power factor is not unnecessarily degraded. Moreover, under certain design constraints, design criteria are developed that ensure the proper choice of various entailed design variables. By using the developed design criteria, the trends of various electromagnetic performances with variation in the slot–pole combination are discussed. The obtained trends clearly show that each slot–pole combination offers a certain torque density and power factor; thus, it serves as a guide for the selection of the slot–pole combination considering the required torque density and/or certain power factor limit. Finally, by using the developed design approach, an SPMVG for rated power of 15 MW is designed; the design objectives are to maximize torque per volume with a power factor limit of 0.4. Moreover, the various aspects of the performances of the designed SPMVG are comprehensively compared against a conventional PM DD 15 MW generator.