設(shè)計(jì)有效的交錯(cuò)功率因數(shù)校正解決方案

　　功率因數(shù)校正（PFC）是必不可少的減輕電能質(zhì)量問(wèn)題，因?yàn)楦嗟膩?lái)源的無(wú)功負(fù)荷連接到電網(wǎng)。在現(xiàn)有的PFC方法，交錯(cuò)PFC方法使工程師建立更緊湊的PFC解決方案，使用較低的成本組成部分，但需要高度復(fù)雜的控制機(jī)制，限制了它的吸引力設(shè)計(jì)師。交錯(cuò)式PFC解決方案基于MCU或?qū)Ｓ肐C集成這些控制機(jī)制，為設(shè)計(jì)者提供了在最終產(chǎn)品實(shí)施高效PFC功能的簡(jiǎn)化方法。

　　定義為實(shí)際功率與視在功率的比值，功率因數(shù)表示運(yùn)行設(shè)備可用的相對(duì)功率。設(shè)備中無(wú)功功率牽引功率因數(shù)遠(yuǎn)低于1。事實(shí)上，沒(méi)有校正，一個(gè)典型的開(kāi)關(guān)模式電源具有約0.6的功率因數(shù)具有相當(dāng)奇數(shù)階諧波失真。當(dāng)功率因數(shù)降到1以下時(shí)，電壓和電流的相位不一致，功率向基波頻率以外的諧波傳播，而這些諧波沿中性線傳播，破壞其他電力用戶。

　　Besides the need for utilities to generate more power to compensate for these inefficiencies， the harmonics create additional losses and dielectric stresses in capacitors and cables. Along with high noise emissions， the related increase in currents in motor and transformer windings lead to early failure of fuses and other safety components. By realigning the voltage and current waveforms so that they are in phase， PFC reduces harmonics required to comply with IEC 61000-3-2， which defines limits on harmonics emitted by electric equipment.

　　PFC methods

　　Although designers can implement PFC with passive components， active power correction allows use of smaller inductors and provides greater flexibility in dealing with different line voltages for products reaching international markets. Active PFC uses a switched-mode converter placed between the input rectifier and the output storage capacitor （Figure1）。 In this approach， a PFC control circuit shapes the input current to match the input-voltage waveform.