Analysis of a Fourth-Order Step-Down Converter

This article proposes a nonisolated wider step-down conversion ratio dc-dc converter having minimum phase behavior at nominal operating condition, for point-of-load applications. Compared to existing quadratic/stacked buck converter variants, the proposed topology shows effective switch utilization at low output voltages, lesser ripple content in source current, and reduced voltage/current stress on components. Time-domain analysis is formulated to anticipate the steady-state converter performance and establish design equations for L-C components. The state-space average model is derived and linearized transfer functions are evaluated to subsequently design a fixed-frequency sliding-mode controller. Step-by-step design procedure is presented to fulfil sliding surface existence, reachability, and stability conditions. Equivalent control law devised in this scheme is duly constituted from source side inductor current dynamics and load voltage error information, so it provides simple realization as well as better transient response. The distinctive features of proposed converter are studied analytically and demonstrated through experimental measurements on a laboratory prototype.