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Analysis of asynchronous machines for direct drive wind power generation

The asynchronous machine is not adopted in direct-drive applications, that is, high-power low-speed applications. The reason is that a machine with a high number of poles is disadvantageous since it often requires a fractional-slot winding, which is unsuitable since it cause high MMF space-harmonics in the air-gap. However, this paper shows that in a doubly fed asynchronous machine, a proper choice of the number of stator and rotor slots minimizes the interaction between stator and rotor MMF harmonics, limiting losses and torque ripple. The design strategy of the doubly fed asynchronous machine is explained and the results are commented, highlighting advantages and drawbacks of the proposed solutions.