Scale models formulation of switched reluctance generators for low speed energy converters

This study presents a design methodology based on scale models for low speed switched reluctance generators (SRG). This study is motivated by the application of SRG to direct-drive wind turbines and other low speed renewable energy systems. In direct drive energy converters considerable simplifications result from the elimination of the gear box which has generally been used to interface a slowly rotating shaft with the generator shaft. The comparison and evaluation of magnetic structures plays an important role in the SRG design. General design methodologies are usually oriented towards the evaluation of stator/rotor poles combinations for regular switched reluctance machines. Besides covering that feature, the formulation of scale laws proposed is also suitable to compare other SRG topologies distinguished by different characteristics of electric and magnetic circuits and their own relative position. In addition, this methodology can be extended to other physical phenomena such as thermal changes and magnetic saturation by introducing some constraints. The running example compares a modular short flux-path topology versus a low speed 20 kW prototype SRG designed for a direct drive wind turbine. The modular topology can optimise the efficiency and weight taking benefits from the significant gain of power per unit of volume and lower losses.