Small signal analysis and control design of current-fed full-bridge isolated dc/dc converter with active-clamp

This paper presents a systematic derivation of small signal model of current-fed isolated full-bridge dc/dc converter with an active clamp. Active-clamp is an active snubber helps to absorb turn off voltage spike across the power semiconductor devices, thus limiting or clamping the voltage across the devices. Inherently, it results in zero-voltage-switching (ZVS) of all devices (main and auxiliary) resulting in low switching losses and higher efficiency. State space averaging technique is used to derive the small signal model. A fixed frequency two-loop average current control with fixed frequency duty cycle modulation is designed to operate the converter for wide variation of load (1:10) and input voltage (1:2). A design procedure is illustrated. Frequency response curves using MATLAB and simulation results using PSIM 9.0 are presented to verify the stability of the control system as well as to observe the transient response with step-change in load and input voltage.