An apparatus monitoring system stability of a DC power system includes a switching power converter with a control loop. The converter is connected to a DC bus of the system. A monitoring loop injected into the control loop includes a sensor circuit monitoring voltage and current of the DC bus and a small signal injector producing a periodic signal with variable amplitude and frequency and injects the periodic signal on a reference signal of the control loop. The monitoring loop includes a stability measurement circuit that varies a frequency input to the small signal injector until the periodic signal has a frequency equal to a system minor loop gain crossover frequency of an impedance ratio of a converter closed loop output impedance and an impedance of the DC power system. The monitoring loop includes a measurement output circuit that outputs a DC power system stability margin at the crossover frequency.

Power electronic instrument for continuously monitoring stability and stabilizing a DC microgrid