Accurate mode boundary detection in digitally controlled boost power factor correction rectifiers

This paper presents an accurate mode boundary detection technique for digitally controlled boost power factor correction (PFC) rectifiers. Auto-tuning of the current and voltage control loops as well as estimation of power-stage parameters L and C are accomplished using sinusoidal perturbations injected into the control loops. The estimated L value acquired by this perturbation based tuning process is used to improve the detection of the boundary between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) in the presence of inductance tolerance, thereby minimizing the mode transition effects and reducing the input current harmonic distortion. The proposed approach is verified by experimental results on a 300 W digitally controlled boost PFC rectifier prototype.