Subsystem-interaction restraint in the two-stage DC distributed power systems with decoupling-controlled-integration structure

Subsystem interaction is an important issue in the two-stage dc distributed power system (DPS) featuring many individually regulated subsystems well designed in their standalone mode. This paper investigates not only the mechanism of realizing the subsystem-interaction restraint with the decoupling-controlled-integration (DI) structure, but also the improvement of DPS´s small-signal stability and the regulated load converter´s input impedance consequent on the subsystem-interaction restraint dependent on DI. DI is different from the conventional integration (CI) structure in that the so-called decoupling operators are developed to map the regulation signal of a source subsystem into the regulation loops of load subsystems. Through classifying the interaction loops in DPS into static and dynamic ones, it is revealed that DI is efficient in eliminating the dominant dynamic-interaction terms in the quasi-static state. Furthermore, with the aid of a three-step impedance criterion, two additional stability-enhancement terms in DPS with DI are picked up. The existence of the stability-enhancement term interprets why an original unstable DPS with CI is possible to become a stable one, provided that the subsystem interaction is restrained through substituting CI with DI. Moreover, as DI is able to improve the low-frequency input impedance character of a tightly regulated load converter, that is, to decrease the negative resistance value or even transform it to a positive one, the possibility of negative impedance instability is definitely decreased.