Small-Signal Stability Analysis and Criterion of Triple-Stage Cascaded DC System

Two individually stable converters are well-known preconditions for discussing the stability of a two-stage cascaded system. However, for a multistage cascaded system, the relationship between its stability and subsystem stability is barely reported due to the lack of modeling method and in-depth stability analysis. In this article, the above problems are solved. First, the generic two-port small-signal model of the multistage cascaded dc-dc converters is established, and its equivalent minor loop gain is calculated, which can be used to assess system stability. On this basis, the stability condition of the triple-stage cascaded dc system is further deduced and compared with its two subsystems. Then, an interesting conclusion is obtained that the whole system may be stable even if some of its subsystems cannot operate stably individually. Besides, according to the deduced stability condition, some existing stability criteria of the triple-stage cascaded dc system are explained uniformly, and a bus equivalent impedance criterion (BEIC) is proposed. Finally, the case study and experiments are carried out to verify the correctness of the theoretical analysis.