Exploring Converter Control Duality in Microgrids: AC Grid-Forming vs DC Droop Control

TL;DR

This paper reveals a fundamental duality between AC grid-forming control and DC droop control in microgrids, providing a unified perspective that bridges their physical and control characteristics.

Contribution

It introduces a novel duality-based framework that uncovers the isomorphism between AC and DC converter control strategies, enhancing understanding and potential control design.

Findings

Demonstrates the duality in small-signal models and control structures.

Shows the duality in power-sharing mechanisms and dynamic responses.

Validates the theoretical duality through simulations.

Abstract

Power electronic converters are fundamental building blocks of both AC and DC microgrids, enabling the integration of renewable energy sources, energy storage systems, electronic loads, and electric vehicles. In contrast, converter control in DC microgrids has developed along the path of droop control, which is widely adopted for decentralized DC-bus voltage regulation and power sharing. Although these control strategies share certain characteristics, their similarities remain largely unexplored due to the distinct physical domains in which they operate. To bridge this gap, we introduce a novel perspective based on the concept of duality to reveal the underlying isomorphism between the two control approaches. We show that AC grid-forming and DC I--V droop control are duals of each other in several aspects, including: (i) the small-signal model of the converter; (ii) the inner current control structure; (iii) power-sharing mechanisms based on the AC swing equation and DC capacitor power balance; and (iv) disturbance signals and dynamic response. Theoretical analysis, validated through simulations on simple converter setups, illustrates these dualities and provides new insights towards a unified control design.