Analysis, design and experimental verification of a field‐modulated permanent‐magnet machine for direct‐drive wind turbines

This paper presents the design and experimental verification of a field‐modulated permanent‐magnet (FMPM) machine using spoke‐magnet outer rotor for direct‐drive wind turbines. The fundamental operation and optimised design process of the proposed machine are elaborated and discussed in detail. The electromagnetic analytical calculation is used for the initial determination of the prototype design, mainly concerning the special constraints of wind power generation, and the two‐dimensional finite element analysis is also applied to optimise and investigate the detailed characteristics. A 5 kW prototype is constructed, and the measured performances have verified the analysis and design, justifying that the proposed machine can offer significant advantages of high‐torque capability and low‐voltage regulation. Experience gained from this study has led to develop a general design guideline for the open‐slot FMPM machine using spoke‐magnet outer rotor for direct‐drive applications.