Analysis of Boost PFC Converters Operating in the Discontinuous Conduction Mode

As power factor correction (PFC) converters for low-power applications usually operate in the discontinuous conduction mode (DCM), operating in continuous conduction mode (CCM) will produce input current distortion. This distortion can be observed in a few switching cycles of one line cycle. Asynchronous switching maps are derived to obtain the time-domain waveforms of input current and output voltage. It can be seen that the cause of the distortion is the change in the current conduction mode. A model for PFC converters operating in DCM with fixed switching frequency and duty-ratio is developed, which can predict the converter operation mode under practical circumstances. Analysis of the output voltage and power limitations is provided based on the proposed model. Simulation and experimental results are presented to verify the proposed method.