Photovoltaic Inverter Controllers Seeking AC Optimal Power Flow Solutions

TL;DR

This paper develops feedback controllers for PV inverters that aim to achieve AC optimal power flow solutions in real-time, ensuring system efficiency and stability while allowing PV owners to participate seamlessly.

Contribution

It introduces a dual epsilon-subgradient based controller design combined with semidefinite programming relaxations to handle non-convex AC OPF problems, with proven convergence under practical conditions.

Findings

Controllers converge globally under diminishing stepsize rules.

The framework accommodates asynchronous updates and faster inverter reference changes.

Applicable to various inverter-interfaced energy resources.

Abstract

This paper considers future distribution networks featuring inverter-interfaced photovoltaic (PV) systems, and addresses the synthesis of feedback controllers that seek real- and reactive-power inverter setpoints corresponding to AC optimal power flow (OPF) solutions. The objective is to bridge the temporal gap between long-term system optimization and real-time inverter control, and enable seamless PV-owner participation without compromising system efficiency and stability. The design of the controllers is grounded on a dual epsilon-subgradient method, and semidefinite programming relaxations are advocated to bypass the non-convexity of AC OPF formulations. Global convergence of inverter output powers is analytically established for diminishing stepsize rules and strictly convex OPF costs for cases where: i) computational limits dictate asynchronous updates of the controller signals, and ii) inverter reference inputs may be updated at a faster rate than the power-output settling time. Although the focus is on PV systems, the framework naturally accommodates different types of inverter-interfaced energy resources.