采用第二級LC濾波器的反激變換器PWM開關(guān)建模
　　　
　在電源上管理輸出電壓紋波是滿足法規(guī)排放要求的方法之一。一個第二階段LC濾波器的有效實施，需要額外的分析和調(diào)整，使電源穩(wěn)定。實現(xiàn)第二級LC濾波器的反激式轉(zhuǎn)換器的設(shè)計可以使用較少的濾波電容，并得到較少的電壓紋波的輸出負載。一個第二級LC濾波器與額外的輸出電容器，以減少電壓紋波是一個較低的成本解決方案，提高了系統(tǒng)的可靠性，因為使用較少的電容器。然而，第二級LC濾波器的補救措施引入了在輸出調(diào)節(jié)的不穩(wěn)定，而不重新調(diào)整補償網(wǎng)絡(luò)。為了解決這個輸出調(diào)節(jié)問題，一個強大的設(shè)計應(yīng)該得到一個小信號模型的開關(guān)功率轉(zhuǎn)換器。推導(dǎo)將在閉環(huán)控制系統(tǒng)中識別開關(guān)電源的極點和零點，這樣就可以獲得總系統(tǒng)行為的直覺，從而優(yōu)化補償網(wǎng)絡(luò)。

　　There are three popular ways to derive a small signal model for Flyback：

　　State Space Averaging method introduced by Middlebrook;

　　PWM switch modeling from Vorperian;

　　Averaged Switch method from Robert Ericsson.

　　The State Space Averaging method has been used for modeling many PWM converters and has been proven to be a useful tool in designing a stable loop. However， since the State Space Averaging method utilizes the parameters like the current signal inside the inductor and the voltage across the capacitor， the derivation work must be redone if any other active components are added. This feature makes the State Space Averaging method not convenient to model the Flyback converter with 2nd stage LC filter.