A General Approach to Synthesis and Analysis of Quasi-Resonant Converters

A method for systematic synthesis of quasi-resonant (QR) topologies by addition of resonant elements to a parent PWM converter network is proposed. It is found that there are six QR classes with two resonant elements, including two novel classes. More complex QR converters can be generated by a recursive application of the synthesis method. Topological definitions of all known and novel QR classes follow directly from the synthesis method and topological properties of PWM parents. The synthesis of QR converters is augmented by a study of possible switch realizations and operating modes. In particular, it is demonstrated that a controllable rectifier can be used to accomplish the constant-frequency control in all QR classes. Links between the QR converters and the underlying PWM networks are extended to general dc and small-signal ac models, in which the model of the PWM parent is explicitly exposed. Results of steady-state analyses of selected QR classes and operating modes include boundaries of operating regions, dc characteristics, a comparison of switching transitions and switch stresses, and a discussion of relevant design trade-offs.