A new small-signal model for current-mode control

A new small-signal model is developed for pulse-width-modulated converters operating with current-mode control. Four different control schemes are analyzed, all of which use the instantaneous value of the inductor current as part of the control modulation. Continuous-conduction mode and discontinuous-conduction mode models are provided.

Sampled-data modeling is applied to the current-mode cell which is common to all converters, and the important results obtained are simplified to give a powerful model for analysis and design. The new model explains all of the observed phenomena of current-mode control, including the subharmonic oscillation which can occur with constant-frequency modulation. It is shown that the model provides transfer functions with three poles for two-state converters. Predictions of the new model are accurate to half the switching frequency.