Small-signal analysis and design of a distributed power system

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Virginia Tech

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.