A reference frame-based microgrid primary control for ensuring global convergence to a periodic orbit

TL;DR

This paper introduces a novel control method for microgrids that guarantees global convergence to a stable periodic orbit, addressing frequency and voltage stability issues caused by renewable energy integration.

Contribution

It extends shifted passivity analysis to limit cycles in microgrids, providing the first global stability proof for non-nominal steady states in full state space.

Findings

The proposed voltage controller ensures stability in a test microgrid.

The method demonstrates smoother transient response compared to standard droop control.

Global attractivity of the periodic orbit is theoretically proven.

Abstract

Power systems with a high penetration of renewable generation are vulnerable to frequency oscillation and voltage instability. Traditionally, the stability of power systems is considered either in terms of local stability or as an angle oscillator synchronization problem with the simplifying assumption that the dynamics of the amplitudes are on much shorter time scales. Without this assumption, however, the steady state being studied is essentially a limit cycle with the convergence of its orbit in question. In this paper, we present a method to analyze the orbital stability of a microgrid and propose a voltage controller for the inverter-interfaced renewable generators. The main hurdle to the problem lies in the constant terms in the rotating internal reference frames of each generator. We extend the shifted passivity of port-Hamiltonian systems to the analysis of limit cycles and prove that, if the system is shifted passive without considering these constant terms, then the periodic orbit is globally attractive. To the best of our knowledge, this is the first global stability result for non-nominal steady states of the microgrid in the full state space, which provides new insights into the synchronization phenomenon where the dissipativity of the system ensures convergence. The proposed controller is verified with a test microgrid, demonstrating its stability and transient smoothness compared to the standard droop control.