Three-phase grid-forming droop control for unbalanced systems and fault ride through

TL;DR

This paper introduces a generalized three-phase grid-forming control for VSCs that manages unbalanced conditions and faults, improving stability and flexibility in power systems.

Contribution

It proposes a novel control scheme combining phase-specific GFM controls with phase balancing feedback, enhancing unbalance management and fault ride-through capabilities.

Findings

Enables phase-specific voltage and power unbalance control.

Allows current limiting during unbalanced faults.

Reduces to positive sequence GFM control in balanced systems.

Abstract

In this work, we investigate grid-forming (GFM) control for dc/ac voltage source converters (VSC) under unbalanced system conditions and unbalanced faults. To fully leverage the degrees of freedom of VSCs, we introduce the concept of generalized three-phase GFM control that combines individual GFM controls for every phase with a phase balancing feedback. The proposed control allows trading off voltage and power unbalance under unbalanced conditions, enables current limiting for each phase during unbalanced faults, and reduces to positive sequence GFM droop control in balanced systems. High-fidelity simulations are used to illustrate the properties of the control.