A Unified Passivity-Based Framework for Control of Modular Islanded AC Microgrids

TL;DR

This paper introduces a unified passivity-based control framework for islanded AC microgrids, ensuring stability and modularity across diverse subsystems and loads without explicit equilibrium knowledge.

Contribution

It develops a decentralized controller synthesis method using port-Hamiltonian systems to guarantee equilibrium-independent passivity and stability in complex microgrid configurations.

Findings

Guarantees voltage and frequency stability in complex microgrids

Provides a decentralized control design based on port-Hamiltonian systems

Validates the approach with realistic medium voltage network simulations

Abstract

Voltage and frequency control in an islanded AC microgrid (ImGs) amount to stabilizing an a priori unknown ImG equilibrium induced by loads and changes in topology. This paper puts forth a unified control framework which, while guaranteeing such stability, allows for modular ImGs interconnecting multiple subsystems, that is, dynamic RLC lines, nonlinear constant impedance, current, power (ZIP) and exponential (EXP) loads, and inverter-based distributed generation units (DGUs) controlled with different types of primary controllers. The underlying idea of the framework is based one equilibrium-independent passivity (EIP) of the ImG subsystems, which enables stability certificates of ImG equilibria without their explicit knowledge. In order to render DGUs EIP, we propose a decentralized controller synthesis algorithm based on port-Hamiltonian systems (PHSs). We also show that EIP, being the key to stability, provides a general framework which can embrace other solutions available in the literature. Furthermore, we provide a novel argument based on LaSalle's theorem for proving asymptotic voltage and frequency stability. Finally, we analyze the impact of actuator saturation on the stability results by exploiting the inherent EIP properties of the PHS DGU model. Theoretical findings are backed up by realistic simulations based on the CIGRE benchmark for medium voltage networks.