Stabilization of a cascaded DC system via adding a virtual impedance in parallel with the load converter

For cascaded systems, interactions among individually designed power subsystems may cause the instability of the whole system. Regulating the input impedance of the load converter is an effectively way to solve this problem, however, one big challenge of this method is how to consider the stability of cascaded system and the dynamic performance of load converter together. In light of this, this paper proposes a parallel-virtual-impedance (PVI) control strategy to improve the input impedance of the load converter. The proposed virtual impedance is in parallel with the load converter, via the proposed virtual impedances, the magnitude and phase of the input impedance of the load converter is modified only in a small range of frequency. As a result, this method not only solves the instability problem of the cascaded system, but also keeps a good dynamic performance for load converter. This paper discusses the concept, realization and design consideration of the proposed strategy in detail. Finally, a 100 W cascaded system, which consisting of an LC filter and a 48V-12V buck converter, is built to verify the correctness of the proposed methods¹.