Stability Assessment of Droop Controlled Hybrid Islanded Multiple Subgrids during Power Sharing
This paper investigates the issue of the small-signal stability of Hybrid Islanded Multiple Subgrids (HIMSs) formed by AC Subgrid (ACS) and DC Subgrid (DCS) clusters interconnected through a group of interlinking converters (ICs). Distributed energy resources (DERs) are controlled using a droop-based method. This control mechanism of ICs indirectly adjusts the load power of ACS and DCS using droop gains. Further, power sharing among the ACS and DCS is achieved accordingly. A linearized system model and analysis of autonomous operation of HISs is developed. Further, the eigen value based sensitivity analysis for HISs is presented to assess the impact of change in load condition, IC location, line resistance and dc droop gain value conditions. Furthermore, the sensitivity of system poles to variation in IC droop gain constant is identified. The set of eigen value trajectory plots are included to confirm the movement of system poles. It is found the pole move further inside the negative real plane for increasing power flow from DCS to ACS. Extensive scenarios are presented to demonstrate the system stability under the HIS control strategy with respect to different droop gain constants.