Decoupled Internal Energy Regulation and Inertial Response Provision for Grid-Forming Multilevel-Converter-Based E-STATCOMs

TL;DR

This paper presents a novel control strategy for multilevel-converter-based E-STATCOMs that decouples internal energy regulation from inertial response, enhancing operational flexibility and reducing storage cycling under variable grid conditions.

Contribution

It introduces a control scheme that separates internal-energy regulation from inertial response in DS-MC E-STATCOMs, improving flexibility and storage management.

Findings

Decoupled energy regulation improves storage cycling efficiency.

The control strategy enables flexible operation as STATCOM or E-STATCOM.

Experimental results validate the effectiveness of the proposed method.

Abstract

As power systems accommodate higher shares of renewable generation, short-term power imbalances become more frequent and can manifest as pronounced voltage and frequency excursions under low-inertia conditions. E-STATCOMs (STATCOMs equipped with energy storage) offer a practical means to provide both voltage support and fast frequency assistance under grid-forming control. Among candidate implementations, double-star multilevel-converter (DS-MC)-based E-STATCOMs enable centralized energy-storage integration at the dc link, which improves thermal management and maintainability. Nevertheless, conventional dc-side power-based internal-energy regulation in DS-MCs can undesirably couple loss compensation to the energy-storage path, accelerating storage cycling and constraining operation when the storage is unavailable. This paper introduces a control strategy that assigns DS-MC total internal-energy regulation to the ac-side active-power path, while reserving dc-side storage power solely for frequency support. By decoupling internal-energy management from inertial-response provision, the proposed scheme enables flexible operation as either a STATCOM or an E-STATCOM according to storage availability and mitigates unnecessary storage cycling. The proposed strategy is verified through offline simulations and laboratory-scale experiments.