Five-Terminal Switched Transformer Average Modeling and AC Analysis of PFC Converters

A simple and accurate five-terminal switched transformer average model is proposed and its generalized equations are derived. The proposed model is capable of both time domain and AC analysis of DC-DC, AC-DC, and is especially suitable for single-stage power factor correction (PFC) converters. Unlike other models presented in literature, the proposed switching cell includes the transformer leakage inductance, an intermediate bus input, and still addresses both continuous and discontinuous conduction modes. The model was applied to two topologies, the bi-flyback and the flyboost parallel/series forward converters. The time domain results show great accuracy when compared with the slower and time consuming switching simulation. The AC analysis is also predicted with greater accuracy exposing the dynamics of such converters, a task that was not as easily addressed before when the unique characteristics of single-stage are considered. The frequency domain analysis was also verified with experimental results for the bi-flyback converter. The model is very relevant to isolated flyback converters including the PFC examples provided, which are not as easily or as accurately modeled by other approaches.