Research on slow-scale bifurcation phenomenon of PFC cascade converter

This study reports a new slow-scale bifurcation phenomenon in linear frequency of power factor correction (PFC) cascade converters, which will offer a useful design reference for PFC power application. Compared with the resistive loads analysed before, the stability of PFC cascade converters is studied, which are more complex but practical. This study has introduced the research method that the secondary efficient point-of-load converter can be equivalent to a constant power load. Based on this method, the small-signal model of the whole system is constructed and the characteristic equations are thus derived. Subsequently, the stable boundary is determined when the coefficients of the characteristic equations are positive according to Routh-Hurwitz stability criterion. Furthermore, the time-domain waveforms and phase portraits between the output voltage and the inductor current are given according to numerical simulation and experimental results at different points. Meanwhile, the total harmonic distortion and the fast Fourier transform diagrams are compared to reveal the influence of the bifurcation phenomenon on power quality of the system. The results provide useful information of parameter space for the design and operation of the converter in the desired fundamental stable regime.