Diode rectifier configurations with a multiphase synchronous generator

Abstract

Direct current (DC) power networks are widely used in transport applications, often derived from a synchronous generator and diode rectifier. The use of more than three phases to reduce the DC voltage ripple eliminates the DC filter capacitance and incorporating multiple phases into the generator avoids the need for bulky phase‐shifting transformers. Recent trends have moved away from high phase‐number machines to multiple winding sets, in order to enhance fault tolerance. This study shows how the number and arrangement of these phase sets and rectifier circuits should be selected to improve steady‐state performance, by suppressing unwanted harmonics. Complex harmonic analysis expressions are developed for the wound field, salient, synchronous generator incorporating both saliency and saturation, allowing general design principles for avoiding circulating harmonic currents and high peak diode currents to be identified. The model is validated on a 15‐phase, 19kVA laboratory machine, reconfigurable as five 3‐phase sets and three 5‐phase sets. The results show that for this example, multiple 3‐phase, winding sets can give better performance than the high phase‐number system, with lower stator copper loss and higher power factor.