Bifurcation Analysis of a Current-Mode Controlled DC Cascaded System and Applications to Design

In an electrical system, dc-dc converters are the major constituents that control the power flow among various terminals including power sources, buses, and loadings. Stability of these constituent converters under all operating conditions is vital to the operation of the electrical system. In this article, a simple dc cascaded system consisting of two cascading averaged current-mode-controlled dc-dc converters is considered. Application of the impedance criteria allows fast and decoupled design of a stable cascaded system. However, the usual impedance criteria fail to predict the stability of the system correctly. Slow-scale instability has been observed from full-circuit simulations, discrete-time analysis, and experimental measurements. The complex behavior caused by the slow-scale instability such as border collision has been analyzed in depth based on the discrete-time model. Stability boundaries are derived in practical parameter space. Finally, effective methods for ensuring the stable design of current-mode-controlled cascaded dc converter systems are discussed.