Comparative Studies of Common Fix-Frequency Controls for Reference Tracking and Enhancement by End-Point Prediction

This paper analyzes the dynamics of reference tracking in switched-mode power converters in terms of both large-signal and small-signal perspectives. Common control schemes, namely, voltage mode, current mode, and V²-control, are compared for their performance in reference tracking. For small-signal analysis, loop gains and reference-to-output transfer functions are analytically derived and verified by the proposed Matlab-based frequency response simulator. In the case of multiple-loop control like V²-control, different loop gains are clarified for their application in load transient or reference tracking. Practical circuit-level design considerations are given to current-mode control for achieving fast reference tracking, while end-point prediction (EPP) is used to improve V²-control, which is inherently slow in reference tracking. The effect of EPP on transfer function is then explained in details. A V²-controlled buck converter with EPP is fabricated. The measured reference-tracking response shows ten times improvement in tracking speed and verifies the effectiveness of EPP in V²-control.