The paper research small - signal model of pfc circuit and build the simplified average - small - signal model of the system . the thesis develop design method of pi regulators which are applied in double closed - loops system . furthermore , the sampling algorithm of votage and current variables is also analysed in this paper 文中對pfc電路的小信號模型進行了研究,并建立了系統的簡化平均小信號模型,在此基礎上,以系統的動態特性和穩定性為設計指標,具體給出了雙閉環系統中pi調節器的設計方法。