Sampled-Data and Harmonic Balance Analyses of Average Current-Mode Controlled Buck Converter
For power electronics engineers designing buck converters, this work provides improved stability analysis tools, though it is incremental as it extends existing sampled-data and harmonic balance techniques to a specific control scheme.
The paper analyzes dynamics and stability of average current-mode control in buck converters using sampled-data and harmonic balance methods, deriving an exact model and a new continuous-time model with frequency response matching experimental data. It identifies an unstable window for the current-loop compensator pole and proposes an S plot to predict subharmonic oscillation and guide pole assignment.
Dynamics and stability of average current-mode control of buck converters are analyzed by sampled-data and harmonic balance analyses. An exact sampled-data model is derived. A new continuous-time model "lifted" from the sampled-data model is also derived, and has frequency response matched with experimental data reported previously. Orbital stability is studied and it is found unrelated to the ripple size of the current-loop compensator output. An unstable window of the current-loop compensator pole is found by simulations, and it can be accurately predicted by sampled-data and harmonic balance analyses. A new S plot accurately predicting the subharmonic oscillation is proposed. The S plot assists pole assignment and shows the required ramp slope to avoid instability.