Abstract

Microgrids are low-voltage electrical networks composed of distributed generation, storage, load, and managed autonomously from the larger utility grid. Modeled after the hierarchical control architecture in bulk power systems, a layering of primary, secondary, and tertiary control has become the standard operation paradigm for microgrids. Despite this superficial similarity, the control objectives in microgrids across these three layers are varied and ambitious, and they must be achieved in real-time without time-scale separations, without centralized decision makers, and ideally in a model-free fashion. In this seminar, we explore different control strategies for these three layers and illuminate some possibly-unexpected connections and dependencies among them. We build upon decentralized primary droop control strategies and motivate the need for additional secondary regulation. We find that distributed averaging-based secondary control architectures using communication among the generation units offer the best combination of flexibility and performance. We further leverage these results in tertiary-level energy management tasks such as an economic generation dispatch. Surprisingly, we show that the minimizers of the economic dispatch optimization problem are in one-to-one correspondence with the set of steady-states reachable by droop control. This equivalence results in simple guidelines to select the droop coefficients, which include the well known criteria for power sharing. Finally, we stress the idealistic assumptions underlying any droop-based control architecture and propose a virtual oscillator control paradigm that contains droop control in the asymptotic limit. We illustrate the performance and robustness of all of our designs through hardware experiments.