Monitoring the stability of DC distributed power systems

In a DC distributed power system, the system level small-signal stability is determined by the minor loop gain, which is an impedance ratio of Z_o/Z_i between the source and load power modules. This paper proposes a practical method to monitor the stability margin of DC distributed power systems. By injecting a small-signal external perturbation current iˆ_p into the DC bus and measuring the response current iˆ_s of the source module/subsystem, the distance between the minor loop gain Z_o/Z_i and the (-1,0) point in the S-plane can be figured out as S(ω)=|iˆ_p(jω)/iˆ_s (jω)|. Consequently, the system stability margin can be monitored by checking whether the inequality S(jω)>½ is valid or not. Both simulation and experimental results demonstrate the effectiveness of the proposed method