A survey on a novel double-rotor spoke-type permanent magnet induction generator employing bridged and bridgeless structures

Double-turbine systems offer a higher capability of wind energy conversion compared to single-turbine systems. Therefore, in order to improve the performance of double-turbine systems and eliminate mechanical gearbox systems by utilizing the direct-drive concept, a new direct-drive generator design is required. In this paper, the structure of a novel spoke-type permanent magnet induction generator (STPMIG) exploited in double-turbine wind systems is investigated, and the performance and relationships of the proposed generator with and without iron bridges are studied. The proposed generator consists of a stator, and two concentric permanent magnet and squirrel-cage rotors, in which the voltage induction in the stator windings is possible only by the permanent magnet outer rotor. Although utilizing the permanent magnet rotor with iron bridges enhances the mechanical strength, the leakage flux increases, which leads to the reduction in the generator output power. In order to decrease the leakage flux and improve the output power of the proposed generator, the bridgeless outer rotor structure is preferred over the rotor with iron bridges. The bridgeless structure offers lower leakage flux, higher efficiency, and lower voltage regulation in comparison with the bridged structure. Furthermore, the novel structure of double-rotor STPMIG allows rotors to rotate independently at different speeds without employing additional rings and brushes, regarded as considerable merit for double-turbine wind systems. Finally, a 250-W bridgeless double-rotor STPMIG exploited in double-turbine systems is constructed and tested to verify the finite element analysis (2D-FEA) results.