Impedance Based Stability Analysis of DC Microgrid

As the number of power electronic converters in a microgrid increases, the stability of the system is compromised due to the undesirable small signal impedance interaction between different types of converters hence present. While the parameters of the individual converters are determined by performing stability analysis of various small signal transfer functions, it is not guaranteed to achieve sufficient stability margin on the microgrid level due to the impedance dynamics introduced by the closed-loop control system of these converters. To this end, the proposed work has developed a closed loop input and output impedance transfer function of a DC microgrid by splitting the microgrid into two subsystems namely the source and load subsystems. The source and converter regulate the DC microgrid voltage from the source subsystem whereas the remaining components are included in the load subsystem. The closed-loop transfer functions of the subsystems are then analysed with the Nyquist criterion to check the stability of the DC microgrid. The studied DC microgrid system has four sources which are PV, PMSG - Wind turbine, battery energy storage system (BESS), and three-phase utility grid. Moreover, DC and AC loads are also considered.