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

Abstract

Flux reversal permanent magnet generators are well suited for use as wind turbine generators owing to theirhigh torque generation ability and magnetic gear. However, they suffer from poor voltage regulation due to their highwinding inductance. In this paper, a design optimization method is proposed for flux reversal generators in wind turbineapplications. The proposed method includes a new multiobjective function. Cost, volume of the generator, and massof 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 optimizationprocedures as a constraint and analyzing the optimization results for different values of it. Also, for the first time, theequations for permanent magnet sizing are considered based on a demagnetization curve for designing a flux reversalgenerator. For this purpose, a step-by-step design procedure is proposed and sensitivity analysis is performed to determinethe sensitivity of output parameters to specific electrical loading, the height of the permanent magnets, and the machinelength-to-diameter ratio. Then a multiobjective optimization based on a genetic algorithm is carried out and the bestcombination of pole number and number of slots/pole/phase is obtained. Then, for this combination, the optimumvalue of the constraint is obtained, too. Then specifications and dimensions of the optimum flux reversal machine as awind turbine generator is presented. Finally, a time-stepping finite element method is used to validate the design andoptimization results.