High-efficiency low-volume starter/alternator for automotive applications

The amount of electric and electronic equipment in automobiles has grown continuously bringing generating requirements more in line with starting requirements, thereby increasing the appeal of combined starter/alternator (S/A) systems. As surface mounted permanent magnet machines achieve high torque and power densities, which are very attractive for S/A applications, this paper outlines the solutions adopted for the development of a direct-drive axial-flux PM (AFPM) S/A including design characteristics and experimental data taken from a 3 kW prototype. This machine topology, having a reduced axial length and low phase reactance, is particularly suited for S/A systems where reduced room along the engine shaft is available and low voltage drop in generating mode of operation is required. Moreover by using a Litz wire winding good efficiency is reached along the whole operating frequency range.