Control of Instabilities in Resonant Converters Using Half-Period Time Delay Output Feedback

Bifurcation phenomena in power electronic converters lead to undesired instabilities. In this paper, different types of bifurcations are identified, which can occur in a series load resonant converter with the variation of the parameters for example, input voltage, load resistance, and so forth. These instabilities are associated mainly to three different bifurcations: (a) Neimark-Sacker, (b) saddle-node, and (c) symmetry breaking bifurcations. Due to the symmetry property of load resonant converters, a half-period time delay output feedback control is used to avoid all of these instabilities. The ideal time delay is realized by a first-order all-pass-filter. The stability analysis is performed and the values of the feedback gains are determined to identify the stable domain in the parameter space. By identifying the unstable orbits, the analytical stability analysis helps to understand as well as to control the mechanisms of these instabilities, which extends the stability domain of the system. This study can also be extended to other load resonant converters where the symmetry property naturally exists.