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 our 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.