Input impedance analysis of PWM DC-to-DC converters

Input impedances of pulse-width modulated (PWM) dc-to-dc converters, which dictate the outcome of the dynamic interaction between dc-to-dc converters and their source subsystem, are analyzed in a general and unified manner. The input impedances of three basic PWM dc-to-dc converters (buck, boost, and buck/boost converter) with either voltage-mode control or current-mode control are derived using Middlebrook´s extra element theorem and feedback theorem, and subsequently simplified into approximations using the graphical Bode plot analysis method. Analytical expressions for 24 input impedances are provided in a factorized time-constant form, thereby providing a comprehensive reference for dynamic interaction analyses requiring knowledge of converters´ input impedances. Theoretical predictions of the paper are all supported by experiments performed on experimental dc-to-dc converters.