On the study of stability of an aggregate DC-to-DC power supply system with a cascade connection of two electric power converter modules

The article is devoted to the issues of studying the stability of an aggregated power supply system consisting of two cascaded buck DC/DC converters, each of which has an individual control system based on pulse-width modulation of the first kind and can operate autonomously. One of the important problems solved in the design of such systems is the problem of ensuring their stability. When designing them today, small-signal modeling is mainly used, which is associated with the loss of information about the nonlinearities of the system. The aim of the work is to study the stability of the main operating mode using various approaches. The stability study was carried out: using a small-signal linearized, electrical model; using a nonlinear simulation model in verified software; using a vector-matrix nonlinear dynamic model in the form of a Poincare map.A small-signal linearized electrical model of the object of study and expressions for calculating its parameters are proposed. A map of the system stability regions anda diagram of the output voltage oscillation range are constructed in the space of two parameters. It is shown that the stability boundaries calculated using the small-signal linearized electric model and the vector-matrix nonlinear dynamic model do not coincide. It is shown that a situation is possible when the small-signal linearized electric model shows the instability of the system, and the nonlinear dynamic model demonstrates the stability of the desired dynamic mode. Such situations have not been described in the literature before. The analysis of small-signal frequency characteristics showed that their use does not allow correct analysis of the stability of the aggregated power supply system near the stability boundary, which may be important for high-speed systems.