Sampled-data modeling of the average-input current-mode-controlled buck converter

Average-input current-mode control (AICMC) is a new control scheme for shaping the input current of a buck converter in a high-power-factor rectifier. AICMC is presented along with a continuous-time model that includes sampled-data effects. AICMC is found to be analogous to current mode control (CMC), so existing CMC models are reviewed with regard to the controversies over low-frequency modulator gain and the experimental measurement of loop gain. Two useful modeling approaches which include modulator gain and sampling effects in a continuous model are identified and reviewed. The "Ridley approach" is used to produce a continuous model which exhibits good experimental confirmation on a 100 W 24.5 kHz buck converter. Possible hazards in the implementation of the "digital" method of loop gain measurement are identified, along with the reason the "analog" method does not actually measure the desired quantity.