Disturbance rejection and robustness considerations in DC/DC converters

This paper introduces a disturbance rejection formalism from a modern control theory perspective for modeling DC/DC converters and paralleled converter systems using a nonterminated model. Robustness issues are briefly highlighted together with the development of a framework towards using intelligent control, e.g. fuzzy logic, for paralleled supplies. In this way, using digital controllers, one can implement the control strategies directly by writing code. The expanded modeling technique allows the input voltage and output load to be treated as disturbance signals rather than as parameters as is typically done. The motivation is that a DC/DC converter operates as a regulator and the loop dynamics should reject the line voltage and load current variations, which are actually acting as disturbances. Simulation results are discussed for a single converter as well as a paralleled system, both for resistive and constant power loads. Mathematical simulation results are in perfect agreement with usual circuit simulators results.