A Floquet Theory-Based Stability Analysis Method for Cascaded DC-DC Converters by Combining with the Describing Function of PWM Link

With the wide application of cascaded DC-DC converters in the field of highly reliable power supplies, accurate modeling and stability analysis for cascaded DC-DC converters are very important. In this paper, a Floquet theory-based stability analysis method for cascaded DC-DC converters by combining with the describing function (DF) of pulse width modulation (PWM) link is proposed and a two-stage cascaded buck converters system is taken as an example. In detail, the DF of the PWM link in the frequency domain is introduced and it’s transformed into the time domain. Then the method of combining the DF of PWM link and Floquet theory is proposed for the first time. Following, the proposed stability analysis method, Middle-brook impedance criterion and Floquet theory are applied to the stability analysis of the cascaded buck converter and the stable ranges of three different methods are compared. Finally, simulation and experiment verify the correctness and accuracy of the proposed method. The proposed stability analysis method provides an accurate and simple choice for the stability analysis of multi-stage cascaded converters.