Analysis and Comparison of Frequency Stabilization Loops in Self-Oscillating Current Mode DC–DC Converters

DC-DC converters, used in bidirectional applications such as battery/u-cap hybrid energy-storage systems, usually operate in current mode with a wide range of input and output voltages. Conventional current-mode control schemes, which requires adaptive slope compensation, are not attractive in these applications. In this paper, a class of self-oscillating hysteretic current-mode control (HCMC) schemes with frequency stabilization are analyzed and compared. Among them, the ripple HCMC scheme has the advantages of the inherent access to the average inductor current information, and inherent decoupling between the voltage and the frequency loops. The modeling and design procedure of two frequency regulation methods, namely the phase-locked loop (PLL) and delay-locked loop (DLL), are presented and compared in detail. The analysis is applicable to a range of inductive converters such as buck, boost, and buck-boost. HCMC implemented with a DLL is shown to not only offer comparable bandwidth compared to the PLL, but is also more robust against system parameter variations. The ripple HCMC controllers with PLL and DLL are implemented digitally, and the two schemes are verified experimentally on a 1 MHz 1-2.5 V to 5 V bidirectional boost converter prototype.