DCM Buck-PFC电路的临界电感与波形畸变

The Boundary Inductance and Waveform Distortion of DCM Buck-PFC Circuit

研究了Ｂｕｃｋ 变换器用于功率因素校正时输入电流波形的畸变，找出了功率因数及波形畸变的决定因素；分析了Ｂｕｃｋ－ＰＦＣ电路的工作原理和临界条件，并推导出了临界电感的计算公式，为工程设计提供了计算依据；最后还给出了一个设计实例及其仿真和实验结果。

Power Factor Correction (PFC) to electrical device can improve the efficiency of power grid. Buck converter working at discontinuous conduction mode (DCM) can produce good PFC performance [1～3] . We present a method to further improve the PFC performance of Buck converter. We derived eq.(8) as the formula of boundary inductance to maintain Buck converter at DCM state, and eq.(10) as the formula of power factor. Eq.(10) indicates that the power factor is determined only by the duty cycle. Since the decrease of power factor is caused by input current waveform distortion, we can infer that the distortion is determined by the duty cycle. It means that decreasing the duty cycle can reduce the distortion, thus increase the power factor. We have not yet found anything similar to eq.(8) and eq.(10) in the open literatures. Results of SPICE simulation (Fig.3 and 4) and experiment (Fig.5) show that the input current waveform is similar to a standard sine wave, and is synchronous with input voltage, but still has some distortion. The computed power factor is 0.99.