The stability of aircraft D-C power systems with inverter loads

THE ANALYSIS presented in this paper is intended to provide a basis for investigating the effects of inverter loads on the stability of aircraft d-c power systems. There have been occasions when energizing a particular inverter has produced an unstable system. In the past, such a situation has been resolved, with varying degrees of success, by an arbitrary change in the time response of one or more of the offending elements. The problem has been subjected to several intuitive explanations, probably the most popular of which is that the time constant of the inverter and the time constant of the generator were the same. While such reasoning is intuitively correct, it is scientifically meaningless, and provides little or no guidance to the system designer. Since inverter-induced instability is a system problem, it must be analyzed on a system basis. The objective of this paper is to perform a system analysis, and to point out the measurable properties of the system which may be used to predict stability.