Near-null response to large-signal transients in an augmented buck converter: A geometric approach

Santanu Kapat, Pradeep S. Shenoy, Philip T. Krein

Research output: Contribution to journalArticlepeer-review


The maximum closed-loop bandwidth of a dc-dc converter is restricted to a fraction of its switching frequency when governed by a conventional average-based pulsewidth modulation (PWM) controller. Even an advanced geometric control is limited by internal slew rates. The bandwidth can reach or exceed the switching frequency through converter augmentation; however, this requires a nonlinear control algorithm and circuit arrangements. This paper considers methods of augmentation and control for a fast buck converter. Conditions for time-optimal transient recovery are obtained for both instantaneous and delayed transient disturbance detection. Design tradeoffs and control issues related to augmentation are considered here. The main switch is controlled using a fixed frequency PWM current-mode control with load current feedforward, and augmented switches are controlled using frequency-limited bang-bang control based on a geometric approach. A small-signal model is obtained and extended control bandwidth is demonstrated. Fast transient recovery is achieved for both single- and two-resistance augmentation. A prototype augmented buck converter is tested. Output voltage and inductor current overshoot and undershoot can be lowered more than with previous methods. It is possible to achieve near-null response in the sense of ripple band to a large-signal transient.

Original languageEnglish (US)
Article number6111490
Pages (from-to)3319-3329
Number of pages11
JournalIEEE Transactions on Power Electronics
Issue number7
StatePublished - 2012


  • Augmented buck converter
  • high bandwidth
  • near-null response
  • ultrafast dynamic performance

ASJC Scopus subject areas

  • Electrical and Electronic Engineering


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