Machine design problems are often solved under the assumption of no-load when calculating iron flux densities. However, it is particularly important to account for the fluxes from the stator currents, the armature reaction, in fractional-slot machines. The fluxes from the permanent magnets and the armature reaction both vary in time with the electrical frequency. By studying the flux that flows along the stator yoke behind every slot in such a machine, it is revealed that the armature reaction flux does not have the same amplitude behind all slots. In addition, it is revealed that the time-varying no-load and armature reaction fluxes are shifted in time, with different phase shifts behind different slots. The sum of the no-load and armature reaction fluxes, namely, the load flux, depends on both the amplitudes of the fluxes and the phase shift between them. The resulting load flux behind each slot varies significantly. In four investigated machines, the ratio of the highest to the lowest load flux amplitude ranges between 1.6 and 6. The load flux can be significantly higher than the no-load flux. The flux calculations are verified through finite-element analysis in all four machines, and the error in the maximum load flux ranges between 2% and 6%.

Abstract.Marine current power is a significant energy resource yet to be exploited for electricity production. Several novel turbine technologies can be found on the market, and new ones emerge every year. This study found that the most popular choice seems to be the axial flow three-bladed turbine, although the industry has not yet converged to one preferred technology. An overview of the turbine technologies is presented with drive train layout for each device, if this information is obtainable. The majority of manufacturers use geared (mechanical or hydraulic) solutions, and an induction or a synchronous generator. The few direct drive systems all use PM synchronous generators. For prototype turbines there is a trade-off between choosing a proven generator technology that is not optimised for the application, and using a prototype machine that may reduce the number of design iterations.

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Abstract-An optimization of an analytical problem with nine variables is executed to find the optimal Permanent Magnet(PM) generator for a tidal turbine. A gradient based solver is used to find the minimum cost of active materials for the given design specifications. The MATLAB function fmincon is used, and the possible minimization algorithms available for this function are compared. As these solvers are only able to find a local minimum, a search is performed trying to find other minimas, both using a MultiStart procedure and using a Genetic Algorithm (GA). Losses are calculated for windings, stator laminations and rotor magnets and solid steel, and a constraint is put on efficiency. The cost effect of varying this constraint is investigated. Optimizations are done with both weight and material cost as objective function, and the different resulting designs are presented.

The aim of this work is to find the maximum torque density limit of a surface cooled SPM machine. In this paper, an analytical and a FEM-based model are developed under some theoretical conditions. Both models consist of a magnetic and a thermal part, where they are used to calculate the torque and the temperature distribution, respectively. Each model is then combined with an optimization process in order to maximize the torque density. The analytical model utilizes the GlobalSearch algorithm (GSA), while the FEM-based one uses the Pattern-Search (PS) approach. A case configuration is selected, and the results between the two models are presented and compared. It is shown that it is possible to determine a maximum limit for the torque density of a machine and the configuration used to get it. A parametric sensitivity analysis is carried out to analyze the influence of some typical parameters on the maximum torque density. Finally, this maximum limit is compared against typical SPMs.