Line-Frequency Instability of PFC Power Supplies

Typically, a power-factor-correction (PFC) power supply consists of two stages, one responsible for PFC and the other for voltage regulation. In this paper, we propose to use a constant power sink to represent the voltage regulating stage, resulting in an analytically tractable model that is able to predict the period-doubled oscillations at line frequency that are not detectable by other conventional models. Using a generalized averaging approach, we investigate the low-frequency dynamics and derive closed-form stability conditions that accurately locate the stability boundaries on selected parameter planes. The model can be conveniently used to evaluate the performance of PFC power supplies, such as harmonic distortion and power factor. Experimental results are presented to verify the model.