Instability in Peak Current Mode Controlled Coupled SIDO Buck Converter

This paper investigates the switching instability, also known as sub-harmonic oscillation of coupled inductor single-input dual-output (CI-SIDO) buck converter under peak current mode (PCM) control. The instability is predicted by developing an accurate small-signal model for PCM controlled CI-SIDO buck converter. The exact small-signal model is developed by using current modulator equations in the state-space model of CI-SIDO buck converter. The current modulator equations define the duty ratios as a function of the circuit variables and are the one that predicts the instability. It is observed that instability in CI-SIDO buck with PCM occurs when both or any one duty ratios are greater than 0.5. The instability is verified using MATLAB simulation results.