Alternative Bridge Spoke Permanent Magnet Synchronous Generator Design for Wind Power Generation Systems

Generators are a key technological element of wind power generation systems. The use of synchronous generators that employ heavy rare-earth permanent magnets is increasing owing to the demand for higher efficiencies. However, these magnets are expensive and undergo an unbalanced supply and demand. Therefore, spoke-type structures have been developed and used in various fields to compensate for the deficient performance when using a ferrite magnet, which is inexpensive and provides a stable supply and demand. However, permanent magnet synchronous generators (PMSGs) with adopted spoke-type structures and an output power of 1 kW or higher have not been studied and practically applied sufficiently. Additionally, new designs must consider differences between the target specifications of a generator and wind turbine. In this study, we designed and analyzed the characteristics of an alternative bridge spoke-type PMSG modeling a generator for a 3-kW class wind turbine. We analyzed the performance of the existing spoke-type generator and proposed an alternative bridge spoke shape with an improved performance by removing the leakage flux of the bridge. The performance of the existing spoke model was compared using the finite element method (FEM), and the performance of the proposed model was verified more accurately by performing a three-dimensional (3D) analysis considering the 3D effect. Additionally, we analyzed the voltage fluctuation rate according to the number of stator slots and overhang structure and designed a final model. Considering the characteristics of the ferrite magnet used in the spoke-type design, the irreversible demagnetization characteristics of the conventional and final models were compared using simulations, followed by a comparison between the stiffness characteristics of the two models. Finally, a prototype was manufactured, and the feasibility of the final design was verified using the performance tests.