Influence of Feeder Characteristics on Hybrid AC/DC Microgrids Stability

Microgrid stability depends on a number of factors, such as the microgrid feeder characteristics, real/reactive power dispatch level, and the load dynamics. This paper focuses on the influence of the feeder characteristics on the stability of hybrid AC/DC microgrids. The line resistance (R), inductance (L), and capacitance (C), parameters highly depend on the rated voltage of the feeder; hence, these parameters affect the active and reactive power sharing of the parallel connected voltage source converters (VSCs). This paper investigates the dynamic stability impact of hybrid AC/DC microgrids having low voltage (LV) and medium voltage (MV) distribution feeders. The transient stability is analyzed by: 1) developing a hybrid AC/DC microgrid with 6.6 kV and 22 kV distribution voltage levels; 2) by applying active and reactive power load switching; and 3) outage of a large distributed energy resource (DER). It is observed that the transient effect due to an active power load switching event on induction motor (IM) rotor speed and system frequency is relatively small for the MV distribution feeder based microgrids, while the impact is larger for the LV distribution feeder based microgrids. The active and the reactive power sharing performance of the parallel operating VSCs depend on the distribution feeder RLC parameters and the load composition that the distribution feeder is supplying.