Mathematical model for split-capacitor push-pull parallel resonant converter in Buck mode

A technique is described whereby a split-capacitor push-pull parallel resonant converter (SC-PPRC) can be operated at a variable switching frequency with zero-voltage switching to provide either a lower (buck) or higher (boost) peak variable output voltage than that which would result in the conventional Normal mode. A comprehensive analysis of the SC-PPRC in the buck mode is yet to be reported. All three modes of operation of the converter are detailed and a mathematical model is presented through which the performance of the converter during the buck mode can be accurately predicted. The proposed buck mode is facilitated by operating the converter essentially at a higher switching frequency than in the normal mode. The higher switching frequency is generated by incorporating a negative and variable time delay into the switching period of the normal mode. In contrast to both normal and boost modes, analysis of the converter in the buck mode is different and complicated by the formation of two different resonant circuits during each switching cycle. The proposed mathematical solution for the buck mode is accurate as validated by both simulations and measured results of a 150-W prototype buck-operated SC-PPRC unit.