Almost Globally Stable Grid-Forming Hybrid Angle Control

This paper presents a new grid-forming converter control strategy, termed hybrid angle control (HAC) that ensures the almost global closed-loop stability. HAC combines the dc-based matching control with a novel nonlinear angle control that resembles the droop control. The design of HAC is inspired by ideas from direct angle control and nonlinear damping injection technique. The proposed HAC is applied to a detailed nonlinear converter model that is connected to an infinite bus via a dynamic line. We provide insightful parametric conditions for existence, uniqueness, and almost global stability of closed-loop equilibria. Unlike in related stability certificates, our parametric conditions do not demand strong physical damping, but they can be met by appropriate choice of ac and dc converter control gains. Finally, we present an implementation of the HAC and illustrate the behavior of the closed-loop system with a publicly available numerical example.