Reduction of permanent magnets in small-scale wind turbines

Small scale wind turbines offer an attractive method for electrification of remote locations using a renewable source of energy. The popular permanent magnet axial flux alternator design for small turbines published by Scoraig Wind Electric has been widely constructed using readily available materials, but requires a relatively large amount of costly rare earth magnets. The prohibitive magnet cost is a result of an ironless stator, which serves to eliminate cogging torque but ultimately introduces a large air gap in the magnetic circuit. This paper investigates the use of powered iron and other ferrous materials to fill the centers of concentrated windings in an attempt to balance magnet utilization and acceptable cogging torque. Simple techniques in line with the accessible manufacturing approach for these turbines are proposed. Experimental results using either a ferrous filing based soft magnetic composite or a steel slug configuration embedded in the stator windings are demonstrated. A 50% magnet reduction is achievable while maintaining or enhancing electrical performance with an acceptable increase in cogging torque.