Decentralized Voltage Control of AC Microgrids with Constant Power Loads using Control Barrier Functions

TL;DR

This paper introduces a decentralized nonlinear voltage control method for AC microgrids with constant power loads, ensuring constrained regulation, stability, and bounded operation without saturation devices.

Contribution

It develops a control barrier function-based continuous-time control law with analytic tuning conditions, enabling constrained voltage regulation and stability analysis in microgrids.

Findings

Proven asymptotic stability of the cascaded microgrid dynamics.

Demonstrated bounded operation and convergence through simulations and real-time HIL tests.

Achieved voltage regulation without saturation devices.

Abstract

This paper proposes a novel nonlinear decentralized voltage controller for constrained regulation of meshed AC Microgrid networks with high penetration of time-varying constant power loads. Modelling the load demand as a constantly evolving unknown disturbance, the network model is reformulated in a cascaded structure composed of a nominal, \ie uncertainty-free, and an error subsystem. By adopting a suitable control barrier function, we formulate a continuous-time control law and derive analytic conditions on the tuning parameters, such that the distance between the true and the nominal state trajectories is bounded. Under sufficient conditions, we prove asymptotic stability of the cascaded dynamics with respect to an equilibrium set and also provide an estimate of the region of attraction. In addition, it is rigorously shown that the proposed nonlinear control law enforces constrained regulation around a rated voltage value, without the need of saturation devices. The operation of the closed-loop system is illustrated both via simulation and real-time HIL scenarios, demonstrating bounded operation and convergence to a neighbourhood of the desired reference vector.