Model-Free Optimal Control of Inverter for Dynamic Voltage Support

TL;DR

This paper introduces a model-free control method for inverter-based resources to provide optimal dynamic voltage support during grid voltage dips, without needing grid parameter knowledge, ensuring fast and optimal response.

Contribution

It develops a novel perturb-and-observe based control approach for inverter voltage support that operates without grid model information, with proven convergence and real-world PV system implementation.

Findings

Converges asymptotically to the optimal solution.

Demonstrates fast and effective dynamic voltage support in simulations.

Operates without requiring grid parameter knowledge.

Abstract

Inverter-based resources (IBRs) are required to provide dynamic voltage support (DVS) during voltage dips to enhance the low-voltage ride-through capability. In this paper, we develop a model-free control method to achieve the optimal DVS (ODVS) without relying on the knowledge of grid parameters. Delving into the optimum trajectory of the ODVS problem, it is found that either the current constraint and the maximum active power constraint of IBRs are binding or one of the constraints is binding. This inspires us to search for the optimum in a closed-loop way by a perturb-and-observe (P&O)-based optimum seeking (OS) controller with either the power factor angle or the reactive current being the manipulated (perturbed) variable. The system is guaranteed to converge asymptotically to the optimum provided the stepsize sequence is diminishing and non-summable. The proposed model-free optimal control is finally implemented within a single-stage photovoltaic (PV) system, where dynamic simulations demonstrate the optimal and fast DVS performance