Dynamics and stability of average current-mode control of buck converters areanalyzed by sampled-data and harmonic balance analyses. An exact sampled-datamodel is derived. A new continuous-time model "lifted" from the sampled-datamodel is also derived, and has frequency response matched with experimentaldata reported previously. Orbital stability is studied and it is foundunrelated to the ripple size of the current-loop compensator output. Anunstable window of the current-loop compensator pole is found by simulations,and it can be accurately predicted by sampled-data and harmonic balanceanalyses. A new S plot accurately predicting the subharmonic oscillation isproposed. The S plot assists pole assignment and shows the required ramp slopeto avoid instability.
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