Impedance specifications for stable DC distributed power systems

In a DC distributed power system, the interaction between individually designed power modules/subsystems may cause the instability of the whole system. In a small-signal sense, system level stability is determined by the impedance ratio Z_o/Z_i. Here, Z _o is the output impedance of the source module/subsystem, and Z_i is the input impedance of the load module/subsystem. As a result, an effective way to prevent system instability is defining impedance specifications for modules/subsystems. This paper briefly summarizes existing works and introduces the authors´ contribution in defining impedance specifications. A new forbidden region for impedance ratio Z_o/Z_i on the S-plane is proposed as the system stability margin requirement. Based on this proposed forbidden region, the impedance specifications of individual loads are established. Further, a very practical measurement approach is developed to examine whether or not the system stability margin requirement of the forbidden region is satisfied