Design optimization of a novel scale-down hybrid-excited dual permanent magnet generator for direct-drive wind power application

This paper presents a novel scale-down hybrid-excited dual permanent magnet (PM) generator for direct-drive wind power application. Two sets of consequent-pole PMs are used in the proposed design, with one on the outer stator and the other on the middle rotor. PMs are separated by iron poles one by one, to form the magnet-iron sequences, which can provide PM excitation and flux modulating simultaneously. Since both the outer stator and middle rotor have flux modulating effect, bi-directional flux modulating can be achieved. Besides the fundamental field components, some other major field harmonics are also synchronous due to the bi-directional flux modulating effect, and these harmonics can contribute to the electromagnetic generation. Therefore, the proposed machine can achieve high torque density and suitable for direct-drive applications. Field windings are employed on the outer stator, so the air-gap field can be easily regulated by controlling the dc current. Hence, the proposed generator can maintain constant output voltage when the wind speed varies. Finite-element method coupled with genetic algorithm is used to optimize a scale-down design of the proposed generator, and its electromagnetic performances are studied in detail.