AC Input Current Distortions and Compensation Schemes of PFC Stages Working in Critical Conduction Mode

Power factor correction in critical conduction mode with valley switching and frequency limitation implicates AC input current distortions. This is especially true at lower power level or higher AC input voltage. The mechanisms resulting in these distortions are illustrated and proper compensation methods are proposed. Furthermore, the influence of the EMI filter capacitor on the AC input current around the AC zero crossings is discussed. All presented solutions are implemented using a highly flexible digital controller.