Ripple determination for switch-mode DC/DC convertors

The state-space average model of a DC/DC convertor is used directly to obtain expressions for the ripple in any state or output of the model. This is used to rederive the current-ripple trade-off conditions in the Cuk convertor in a more straightforward fashion. In addition, it is shown that the buck convertor with input filter inductor and storage inductor coupling, and boost convertor with output filter inductor and storage inductor coupling, have similar ripple behavior to the Cuk convertor at one port when the other port ripple is zero. For the case of equal input and output current ripples, the coupled inductor boost and buck are shown to be superior to the Cuk convertor