Optimisation and design comparison of 10-kW and 3-MW PM flux-switching machines for geared medium-speed wind power generators

The paper details the design optimisation and comparison of two different rare-earth permanent magnet flux-switching machines (PM-FSMs)—12/10 and 12/14—for geared medium-speed wind power generators. The focus is mainly on trade-offs in the performance of these two machines at 10 kW and 3 MW power levels, with highlights on the multi-objective evolutionary optimal performance of small-scale to utility-scale wind turbines. Based on finite element analyses (FEA) and multi-objective design optimisation (MDO), different streams of optimal solutions are obtained and studied. As an indication of the potentials of the proposed PM-FSM wind generators, even for rare-earth-free concepts, the 3 MW designs portray significantly improved torque density thanks to the fixed rotor speed considered at both power levels, and also, smaller torque ripple profiles are conceived due to differences in the calculated saliency ratios, compared to their 10 kW designs. Another finding is based on the nonlinearity of the MDO process on the objective performance of the different machine topologies at the different power levels, which was necessitated by the optimal behaviour of certain design variables such as the split ratio, slot opening width, current density and PM width. Uncharacteristically, the results also reveal possibilities for higher efficiency in 12/14 machines compared to the 12/10 machines, due to positive relationships approximated from general evaluations conceived in the MDO search space in the former, for the split ratio and current density when plotted against the active mass. Lastly, a comparison between 2-D static and 3-D transient FEA processes on some selected benchmarks displayed good agreement.