Understanding the Role of Microgrid Topology for Decentralized Model-Based Control

Abstract

This paper identifies how the topology of a microgrid, particularly with respect to localized power injections, can affect the overall stability of the system. Microgrids are smaller-scale power networks that can disconnect from, and operate independently to, the main grid if necessary; accordingly, distributed and local generation is much more common in these systems. Of these local power sources, a significant proportion interface with the microgrid via inverters, and therefore lack physical inertia. This absence of physical inertia exacerbates the control challenge in a microgrid. These issues motivate the question of how to best control distributed generators to realize grid-wide improvements to power quality. We outline how the placement of controlled distributed generators can result in varying degrees of improved transient behavior, following disturbances to a microgrid. In this resulting simulations and analysis, we find that when the power sources in a microgrid are of varying capacity or rating, then the network topology can have a significant effect on transient performance deterioration. Notably, we find that if even a single a lower rated power source is ‘near’ or adjacent to a grid disturbance, then the microgrid may experience severe harmonic disturbances. In addition, we show that if such sources are controlled with a decentralized optimal controller, rather than a typical droop mechanism, then the overall microgrid performance is significantly improved.