设计有效的交错功率因数校正解决方案

　　设计有效的交错功率因数校正解决方案

　　功率因数校正（PFC）是必不可少的减轻电能质量问题，因为更多的来源的无功负荷连接到电网。在现有的PFC方法，交错PFC方法使工程师建立更紧凑的PFC解决方案，使用较低的成本组成部分，但需要高度复杂的控制机制，限制了它的吸引力设计师。交错式PFC解决方案基于MCU或专用IC集成这些控制机制，为设计者提供了在最终产品实施高效PFC功能的简化方法。

　　定义为实际功率与视在功率的比值，功率因数表示运行设备可用的相对功率。设备中无功功率牵引功率因数远低于1。事实上，没有校正，一个典型的开关模式电源具有约0.6的功率因数具有相当奇数阶谐波失真。当功率因数降到1以下时，电压和电流的相位不一致，功率向基波频率以外的谐波传播，而这些谐波沿中性线传播，破坏其他电力用户。

　　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.