OPTIMISATION OF A CLAW-POLE ALTERNATOR USING SOLID COFE ROTOR
Résumé
INTRODUCTION Claw-pole alternator is often used in automotive industry because of its easy process of fabrication and its low cost. Permanent magnets are currently integrated to increased its efficiency, however their higher price brings into question their usage. This tight context implies finding new technical solutions to keep the same efficiency without magnets. One of these solutions is to use unusual soft magnetic materials like CoFe [1]. Fig. b shows magnetizing curves of different CoFe tested in the solid rotor in order to evaluate their potential gain. OPTIMIZATION OR PREDESIGN Unlike conventional electrical machines, claw-pole machine is characterized by its unsymmetrical shape of poles along the rotor that induces a 3D flux path (Fig. a). In this context, a model based on a magnetic equivalent circuit (MEC) is established to perform optimizations under constraints including short time simulation and high parameters number [2] [3]. In this case, the model accuracy is about 30 % but it's adequate to achieve predesign of the alternator. Optimization aim is to increase the output current under load condition and 1800 rpm. Fig. c present all predesign results for each CoFe. They are obtained with both the MEC model and a parametric FE model in order to improve the estimation accurate and to complete the predesign analysis. Results demonstrate the CoFe ability to increase the output current at low speed. CONCLUSION Alternator predesigns achieved with the MEC model showed that using solid CoFe rotor should increase the current flow of 30 % to 70 % at low speed.