Fast scale instability problem of cascaded buck conversion system and its phase-shifted-carrier solution

Cascaded Buck conversion system is a typical structure in dc distributed power system (DPS). It is known that, the interaction between its individually designed power modules/subsystems may cause the instability problem of the whole system. The traditional solution is to design this system by Middlebrook criterion. However, authors found that, even if the entire system meets Middlebrook criterion, the fast scale instability problem may still occurs. In order to analyse and solve this problem, this paper presents a fast scale model for the cascaded buck conversion system. By this model, the essential reason for fast scale intsability problem is explained and a phase-shifted-carrier (PSC) solution is also proposed. Finally a 48 V-24 V-5 V 200 W cascaded system is built, and the experimental results confirmed the theoretical analysis.