Research on Low-Scale Bifurcation of PFC Operating with a Cascade Buck Converter

Power factor correction (PFC) converters possess high complexities due to the introduction of the series connections among power converters, which adversely affects the stability of the PFC system. On the assumption that the input voltage can be replaced by its RMS value, and the frequencies of the inductor current and the output voltage of PFC primary converter are much lower than the switching frequency of the converter, the simplified analytical circuit of the PFC cascade converter is established with average current control. As for PFC cascade converter, the secondary converter can be equal to a constant power load, based on which the small-signal model of PFC cascade converter is constructed and the low-scale bifurcation in PFC cascade converter is revealed. Based on the small- signal model, the transfer function and the characteristic equation are derived to determine the stable boundary according to Routh-Hurwitz stability criterion. The time-domain waveforms and Lissajous phase trajectories between the output voltage and the inductor current are given. Furthermore, the total harmonic distortions (THD) before and after bifurcation are comparatively analyzed to reveal the influence of the bifurcation phenomenon on power quality of the system. Finally, a simulation model is designed, and its simulation results agree very well with the theoretical analysis.