Power Control of Converters Connected via an L Filter to a Weak Grid. A Flatness-Based Approach

TL;DR

This paper presents a flatness-based nonlinear control strategy for power converters connected to weak grids, ensuring stability and safe operation through robust estimation and analysis, with simulation validation.

Contribution

It introduces a robust flatness-based control method for weak grid connection, including a notch filter for PCC voltage estimation and stability analysis for unknown grid impedance.

Findings

Controller maintains stability in weak grid conditions

Notch filter effectively estimates PCC voltage

Simulation confirms robust performance

Abstract

In this article, a nonlinear strategy based on a flatness approach is used for controlling the instantaneous complex power supplied from the Point of Common Coupling (PCC) to a weak grid. To this end, the strategy introduced by the authors in [1] considering a strong grid is robustified for avoiding system instability when the converter is connected to an unknown grid. The robustification method consists of including a notch filter that estimates the PCC voltage and using it to build the controller (i.e. the measured PCC voltage used to design the control strategy for a strong grid is replaced by the PCC voltage estimated with the notch filter). In addition, before designing the controller, the steady-state stability and safe operation limits when injecting complex instantaneous power to a grid of unknown impedance are analyzed. This analysis is independent of the control strategy, and applies to all power injection schemes. Simulations are presented for showing the performance of the proposed controller in presence of a weak grid.