Linear control of the “buck” converter with unknown resistive loads

This article describes the design of an observer-based, robust, linear output feedback controller for the regulation, and output reference trajectory tracking tasks, in switched “buck” converter circuits with completely unknown, time-varying, resistive loads. The disturbance effects of the unknown load resistance are on-line estimated by means of a Generalized Proportional Integral (GPI) observer, which represents the dual counterpart of Generalized Proportional Integral controllers, introduced in Fliess et al.. The reconstructed disturbance complements the controller in a cancelation effort which allows the feedback controller to become a traditional PD controller. The designed average feedback controller is then implemented via a Σ - Δ-modulator, which effectively translates the designed continuous average feedback control input signal into a discrete valued switched input signal driving the converter´s input switch and preserving all relevant features of the average design. The appendix collects some generalities about GPI observers.