Characterizing impedance interactions in switched-mode converters based on linear fractional transformations (LFTs)

Exploiting control engineering tools in power electronics applications would effectively improve modeling and design. This paper presents an alternative approach to formulating the modified transfer functions of dc-dc switched converters due to impedance interactions caused by interconnected subsystems. Switched-mode converter, input filter and load are modeled using the two-port modeling technique, and the reflected transfer functions are characterized by using linear fractional transformations (LFTs). The used method has proved to be simple and more practical than the commonly used approach "Extra Element Theorem". The theoretical predications are supported by computer simulation of a voltage-mode (VM) controlled buck converter operating in continuous conduction mode.