Fixed-Frequency Hybrid Conduction Mode Control for Three-Level Boost PFC Converter

Discontinuous conduction mode (DCM) and critical conduction mode (CRM) have held dominant positions in low-power boost power factor correction (PFC) control. Typically, two-level DCM and CRM suffer from high peak current and variable frequency at several-hundred kilohertz, respectively. The two factors can cause secondary effects such as high electromagnetic interference, current stresses, input filter design difficulty, and switching losses. Only to take merits of DCM and CRM that are fixed frequency and lower peak current, this article utilizes three-level boost (TLB) and its three-level current-slope options. This article proposes a hybrid conduction mode (HCM) control, which adopts adaptive single-switch on-time to achieve fixed-frequency quadrangular CRM operation. At lower input voltage, low inductor current enters DCM so that TLB PFC experiences hybrid operation modes depending on varying ac input. Analyses and experiment results in this article confirm that the proposed HCM control can achieve huge reductions of switching losses and peak current stress, improving efficiency in wide-range input voltage and load at the cost of acceptable PF drop. Moreover, a simple voltage-balancing scheme is implemented to the proposed control and verified effective to resolve the inherent topology issue.