Circuit models of PWM DC-DC converters

A systematic method is presented for including parasitic resistances and offset voltage sources of power switches into averaged dynamic large-signal, DC, and small-signal circuit models of PWM converters operating in continuous conduction mode. This method is based on the principle of energy conservation. It is shown that the equivalent circuits can be manipulated, using the reflection rule, to simplify the models. A procedure of modeling the buck converter is detailed. Models of all buck-derived converters have the same structure as that for the buck converter, but expressions for averaged components are different. These expressions are given. A design equation for selecting the value of the filter capacitance is derived, and it is shown that the ripple voltage can be made dependent only on the equivalent series resistance of the filter capacitor