Stability Issues in Peak-Current-Controlled SEPIC

The aim of this paper is to discuss the impact of passive power components on peak-current-controlled single-ended primary inductance converter (PCC-SEPIC) current loop stability. Stability conditions are determined by means of a novel dynamic model of the PCC-SEPIC, taking into account the difference between the small-signal ac components of the voltage across coupling capacitor and of the input voltage. The analysis of dominant closed-loop poles allowed by the new model highlights the dependence of PCC-SEPIC stability on input and output inductors, coupling capacitor, and current modulator gain and losses. Inductive and capacitive damping approaches are discussed to achieve intrinsic stability of the current loop. In both cases, the damping of dominant poles is investigated by numerical resolution of the new model and design guidelines are provided about how the L-C parameters can be chosen in such a way that oscillations on the voltage across the coupling capacitor are adequately damped. Experimental verifications confirm the validity of predictions provided by the new model.