Optimized Valley Skipping Strategy to Improve Efficiency and Reduce THD for DCM Boost PFC Converter

This article proposes an optimized valley skipping strategy to improve efficiency and reduce total harmonic distortion (THD) for boost power factor correction (PFC) converters in discontinuous conduction mode (DCM). In DCM, the valley skipping strategy is used to reduce the switching ON loss of the power switch. However, conventional skipping strategy causes dynamic changing valleys in a half-line cycle, leading to frequency hopping and extra current distortion. To avoid this, a control strategy based on constant skipping valleys (CSV) is proposed. Firstly, the switching frequency variation with CSV is derived based on the analytical expression of parasitic resonance. Secondly, by employing CSV in control, not only is the switching frequency hopping eliminated, but also the switching cycle corresponds more accurately with the desired cycle. Therefore, an accurate average current control is derived to reduce the current distortion. Thirdly, the CSV is tuned according to a loss estimation, which further improves the efficiency under valley skipping operation. Finally, a 250W prototype is built to verify the proposed control strategy. Experimental results demonstrate that the proposed strategy improves the efficiency by an average level of 0.4% and reduces the input current THD to levels below 3.1% at rated power.