Design Considerations for Permanent Magnet Direct Drive Generators for Wind Energy Applications

Abstract

Permanent Magnet Direct Drive (PMDD) generators offer very high force density, high efficiency and low number of components. Due to these advantages, PMDD generators are getting popular in the wind energy industry especially for offshore application. Presence of permanent magnets gives magnetic field for free but there are many design considerations which must be taken into account for a good design. The design considerations presented in this paper are rotor eccentricity, short circuit current estimation, voltage reflection at generator terminals due to high frequency switching and forces during magnet assembly. Simplified analytical methods which give quick results have been developed and then simulations have been performed to validate the analytical models. FEMM 4.0 which is a Finite Element (FE) solver was used for validation of various magnetic force models. MATLAB® Simulink was used for short circuit and voltage reflection validation. It was deduced that the analytical methods give good estimation of these effects and can thus be included at an early design stage.