Peak-current-mode-controlled buck converter with positive feedforward control

The closed-loop control stability of a switching converter can be compromised when the source voltage is not an ideal voltage source, but presents finite Thévenin impedance. This phenomenon is called source subsystem interaction. As an active approach to improve the stability degraded by the source subsystem interaction, the positive feedforward (PFF) control is proposed for the peak-current-mode-controlled buck converter. PFF control stabilizes the input port in the frequency range where the source subsystem interaction affects system stability, while allowing the feedback controller to maintain tight output voltage regulation at lower frequencies. The approach results in greatly improved stability with a slight reduction of output feedback control bandwidth. Small-signal models are developed based on g-parameter representation. The design technique of the positive feedforward controller is discussed. Also, the total system stability is analyzed based on the unified impedance criterion. This approach is validated by simulation.

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