Input Filter-Based Ripple Injection for Mitigating Limit Cycling in Buck Converters Driving CPL

In a two-stage dc-dc intermediate bus architecture (IBA), an LC input filter with a series parasitic resistance is often used in an intermediate bus converter (IBC) because of its discontinuous input current, which is designed using Middlebrook's impedance criteria. Using the ripple voltage of the input filter capacitor, this article proposes a closed-loop pulsewidth modulation (PWM) control method in the IBC to mitigate limit-cycle oscillations (LCOs) in an IBA. This ripple voltage is shown to indirectly carry inductor current information of the IBC and offers a virtual damping in the closed-loop system. Small-signal models are derived, and stability conditions are established. A simple PI controller is shown to be sufficient to achieve tight output voltage regulation and fast transient response. The proposed technique is extended to a multiphase IBC to achieve equal current sharing among the phases. Hardware prototypes are developed, and the analytical claims are verified using experimental results.