An Improved Homopolar Generator Topology for Reduced DC-Link Voltage Ripple Using Passive Diode Rectifiers

Synchronous homopolar machines, when inter-faced with medium-voltage DC primary distribution via three-phase diode rectifiers, constitute a valid alternative technology to conventional AC/DC electric generation units for hybrid and electric aircraft. Passive power converters feature superior reliability, simplicity, and cost-effectiveness, while the machine's field winding provides a reliable DC-link voltage regulation. Targeting the DC-link voltage ripple reduction, a square-wave back electro-motive force design is proposed. In this paper, the impact of the diode rectifier operation on the generation system output is addressed. In particular, the commutation rules of the rectifier due to the machine's inductance are investigated. Considering the typical layout with two series-connected diode rectifiers, a novel concentrated winding layout featuring a
$\pi/6$
phase shift between the two three-phase windings is proposed, aimed to limit the DC-link voltage ripple due to the simultaneous commutations. A voltage ripple reduction of 25% is achieved when compared to a conventional winding layout: the performance of the two systems is evaluated through 3-D Finite-Element Analysis (FEA) by integrating the diode-rectifiers within the FE circuital environment.