Hybrid-excitation DC machines as highly reliable generators for ram air turbines

Ram air turbines, deployed in the external airflow during flight, are used as emergency power sources to feed the vital apparatuses required for governing aircrafts in case of failure of main supply systems. Such turbines mostly drive electric generators usually connected to a DC bus supported by emergency batteries, which supplies the vital avionic systems. Such generators must then feature high dependability, adequate regulation capability and good overall efficiency. This paper investigates the employ for such purpose of hybrid-excitation DC machines, which may achieve a high reliability thanks to the inherent internal redundancies and to the limited use of electronic components. Referring to a mid-power case-study, a preliminary design and FEM-circuital models purposely developed for validation and design refinement are described, finally reporting and commenting significant simulation results.