Community microgrid: Control structure, design, and stability

Abstract

This work investigates the performance of a community microgrid (C-$\mu$Grid) in an islanded mode of operation. A control structure has been developed, which focuses on transient stability of the primary controllers (PCs) of individual distributed energy resources (DERs) in the community, and also when the DERs work in tandem to balance load and generation. This approach shows a method for decoupling the state vectors of a highly coupled system, so that the system parameters can be regulated separately with accuracy, speed and stability. This work also demonstrates a technique for analysing and minimizing the impact of communication delays, which may exist between two controllers at different hierarchies. Besides, our analysis shows that power transferred between the multiple buses of a C-$\mu$Grid causes voltage variation that is different from traditional power distribution. Accordingly, a power transfer method has been proposed. These aforementioned control designs have been modeled for a C-$\mu$Grid structure that forms part of a modified IEEE 13 bus system, and simulated in real-time using OPAL-RT. A comparative analysis has been performed between DER voltage references provided by traditional optimal power flow (OPF) and our proposed method of power transfer. The simulation results show stable system operation during normal condition, and post delay recovery, when our developed control and power transfer methods are used. However, certain combinations of voltage references provided by OPF destabilizes the PCs and degrades the quality of power injection into the grid. These results have been utilized to characterize the functional requirements of a C-$\mu$Grid Central/Distributed Controller.