Fast-Slow Scale Bifurcation in Higher Order Open Loop Current-Mode Controlled DC-DC Converters

Higher order converters, without an external voltage control loop, have been known not to exhibit a fast-slow scale bifurcation interaction, as the slow-scale bifurcation has generally been believed to be caused by parameter changes in the outer loop. In this paper, it is shown that a current-mode controlled Cuk converter can exhibit an interaction between fast-scale and slow-scale bifurcations even in the absence of this closed outer voltage control loop. The phenomenon is probed using an approach based on the system's monodromy matrix that does not only predict this instability but also provides a systematic method for the development of new control strategies to avoid the onset of this bifurcation. Analytical and numerical results prove that the new controller greatly extends the stable region of operation of the converter.