Source Impedance Analysis of a DC Microgrid under Droop Control

Abstract

The impedance based stability assessment method has been widely used to assess the stability of interconnected systems in different application areas. The output impedance (admittance) of the source subsystem and input impedance of the load subsystem should be obtained before the stability criterion of cascaded system is applied. This paper deals with the analysis of the source impedance for the droop-controlled permanent-magnet synchronous generator (PMSG) system. Transmission cables are also taken into account since it cannot be neglected in the low voltage microgrid i.e., DC microgrid (DC MG). This paper develops the mathematical model of the PMSG system, derives the output impedance of the source subsystem and shows the effect of parameters variation such as droop coefficient, feeder impedance and control bandwidth on source impedance. The aforementioned analytical result is confirmed by time domain simulations.