Keywords: AC-to-DC converter, single-stage converter, small signal, state averaging, power factor correction, DCM, ZVS, signal analysis, feedback compensation network
Small-signal analysis of a single-stage two-switch AC-to-DC converter
Small-signal analysis of a two-switch single-stage AC-to-DC converter is presented using the state averaging technique and low-ripple approximation. Based on the state equations for different intervals of operation, averaged state equations are derived. The averaged state equations for the boost inductor current and tank inductor current are zero leaving only three average state equations corresponding to the voltages across the dc bus, output and the coupling capacitor (that is in series with the tank inductor). Following perturbations and linearisation, AC terms are equated to arrive at the three AC equations. Laplace transforms of these AC equations are used to derive control-to-output and line-to-output transfer functions. Frequency responses of these transfer functions are obtained and they are verified by PSPICE simulation. Based on the analysis, the feedback compensation network is designed for a 500 W, 48 V output prototype converter.