Dynamic analysis of the Class-D converter at fixed frequency using amplitude and phase modulation

A practical small-signal model to predict the dynamic response for closed-loop operation of the Class-D power converter with a variable capacitance switch (VCS) is presented. Although the resonant stage of the power converter can be modeled solely by amplitude modulation, the rectifier stage introduces phase modulation into the dynamic model. A generalized solution matrix is obtained using both forms of modulation which predicts the control-to-output, input-to-output and output impedance responses. Also, the predicted transfer functions agree much better with experimental measurements than those using only amplitude modulation. Theoretical and experimental comparisons are made based on a power converter operating at 350 kHz