Robust Microgrid Clustering in a Distribution System with Inverter-Based DERs

Power electronics for the utility interface of distributed energy resource (DER) offers many benefits in the electric grid operation through flexibility of the DER controls. Energy from various generation sources including renewables can be efficiently delivered to the consumers with high power quality and reliability. However, mixed source microgrids comprising both inverter- and synchronous generator-based DERs are susceptible to collapse, particularly when the system operates in the islanded mode. This paper presents robustness studies on microgrids from a qualitative point of view, borrowing features from ecological systems that are highly robust. The interrelationships between ecological species translate into the dynamic behavior of DERs, affected by their sizes and locations within the grid. The advantage of such qualitative analysis over traditional quantitative viewpoint is it explicitly identifies the nature of interactions and interconnections between the subsystems as beneficial or detrimental to stability. From the robustness studies, the best possible microgrid configurations are determined for IEEE 33-bus system having a mix of inverter-based DERs and synchronous generator-based DERs. Furthermore, all possible microgrid cluster formations are studied for finding the most robust microgrid islanding strategies.