Null response to a large signal transient in an augmented dc-dc converter: A geometric approach

The maximum closed-loop bandwidth of a dc-dc converter is restricted to a fraction of its switching frequency, while governed by a conventional pulse-width-modulation (PWM) technique. Even an advanced geometric control is limited by its internal slew rate. The bandwidth can be made close to (even higher than) the switching frequency through converter augmentation; however, it requires a proper control algorithm and circuit arrangements. This paper considers methods of controlling both augmented buck and boost converters. An augmented boost converter topology is also proposed. The main switch is controlled through fixed-frequency PWM control, and augmented switches are controlled through a bang-bang control. The open-loop small-signal analysis is carried out using a frequency domain approach. Minimum-time transient recovery is achieved using a finite set of augmented resistances and dynamically varying voltage hysteresis bands. It is possible to achieve null response in the sense of ripple band to the large-signal transient.