As one of the important energy conversion systems in renewable energy power generation, the two-stage DC-DC converter cascaded system composed of source converter and load converter has been widely used in industrial applications. Different from the constant voltage load of the traditional DC-DC converter, the load converter in the cascaded converter, as the constant power load of the source converter, has an obvious impact on the stability of the source converter. In this paper, the cascaded system composed of Cuk converter as source converter and buck-boost converter as load converter is studied. Analyses results show that with increasing of power load, a Floquet multiplier of monodromy matrix belongs to the converter cascaded system traverses the unit circle from outside to inside along negative real axis and will suddenly jump out of the unit circle when the power load reaches a specific value. Correspondingly, the entire system gradually moves from period-doubling bifurcation state to period-1 limit cycle and then suddenly jumps to chaos state. With application of monodromy matrix theory and sinusoidal voltage compensation method, stability boundary of the system is extended and nonlinear behaviors are stabilized. Finally, simulation and experimental results verify the feasibility of analytical technique and conclusions.

SummaryA partial power processing non‐isolated bidirectional DC‐DC converter is proposed, which is composed of non‐isolated bidirectional DC‐DC converter and direct power flow path. Part of the power of the system is transmitted from the power stage to the load through the non‐isolated bidirectional DC‐DC converter, while the other part is transferred via the direct path without processing by the non‐isolated bidirectional DC‐DC converter. This topology not only enhances the energy conversion efficiency but also has the remarkable advantages of high energy density, simple design, small volume, light weight, and low electromagnetic interference. It can be applied in various two‐way energy management scenarios such as photovoltaic, fuel cell, and super capacitor energy storage. The analysis of the operating principle reveals that the converter can realize the increase and decrease of input voltage and the bidirectional flow of current. When the bidirectional DC‐DC converter steps the voltage down, the partial power converter is in the step‐up mode of reverse transmission. As the bidirectional DC‐DC converter is steps input voltage up, the partial power converter is in step‐down mode of forward transmission. The differential equations and mathematical models of each operating mode are established, and the appropriate voltage feedback control strategy is proposed. Finally, a prototype is constructed and experiments verify the analysis.