Optimal design of a flux reversal permanent magnet machine as a wind turbine generator

Flux reversal permanent magnet generators are well suited for use as wind turbine generators owing to their high torque generation ability and magnetic gear. However, they suffer from poor voltage regulation due to their high winding inductance. In this paper, a design optimization method is proposed for flux reversal generators in wind turbine applications. The proposed method includes a new multiobjective function. Cost, volume of the generator, and mass of the permanent magnet are considered in it independently and simultaneously. Besides the new objective function, the main superiority of this paper compared with published papers is considering winding inductance in optimization procedures as a constraint and analyzing the optimization results for different values of it. Also, for the first time, the equations for permanent magnet sizing are considered based on a demagnetization curve for designing a flux reversal generator. For this purpose, a step-by-step design procedure is proposed and sensitivity analysis is performed to determine the sensitivity of output parameters to specific electrical loading, the height of the permanent magnets, and the machine length-to-diameter ratio. Then a multiobjective optimization based on a genetic algorithm is carried out and the best combination of pole number and number of slots/pole/phase is obtained. Then, for this combination, the optimum value of the constraint is obtained, too. Then specifications and dimensions of the optimum flux reversal machine as a wind turbine generator is presented. Finally, a time-stepping finite element method is used to validate the design and optimization results.