A small-signal analysis of a two-stage distributed power system is performed. Although the
distributed power system is composed of conventional PWM converters, the analysis methods
can be extended to systems using other converter topologies. The analysis focuses on two
important features of a two-stage distributed power system: parallel power modules and cascaded
regulators.
The small-signal characteristics of parallel module regulators are analyzed, and an expression
for the loop-gain of a parallel-module system is obtained. It is found that a parallel
module system can be configured so that the loop-gain of the system is independent of the
number of modules.
The effects of placing switching regulators in cascade are analyzed. Of primary concern is the
effect of the second stage's dynamic impedance on the first stage's control loops. It is found
that the negative dynamic resistance of the second stage gives rise to right-half-plane poles
in the opened-loop gains of the first stage. Fundamental loop-gain analysis is used to determine
that stability of the system. It is found that the first stage of a cascaded regulator system must satisfy additional design constraints in order to be stable while driving a negative dynamic
resistance.
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