Asymmetrical Oscillations in Digitally Controlled Power-Factor-Correction Boost Converters

Digitally controlled power-factor-correction (PFC) converters are essentially piecewise-smooth nonlinear systems due to their switching action. However, their complex behavior almost remains unexplored. Unlike analog control, digital control introduces a time delay due to the sample-and-hold and the digital computation. Here, a small-signal model that takes the time delay into account is derived to judge the stability of a digitally controlled PFC boost converter. It is proven that the time delay seriously degrades the converter's stability. After the inner current loop and/or the outer voltage loop lose stability, we experimentally discover that oscillations begin to occur, and the oscillations are asymmetrical. Such an asymmetry can be interpreted by the underdevelopment characteristic of the dynamical behavior in the digitally controlled PFC boost converter. The results reported in this brief offer more knowledge about the dynamical behavior in digitally controlled PFC converters.