Grid-Forming Hybrid Angle Control and Almost Global Stability of the DC-AC Power Converter

Abstract

This paper introduces a new grid-forming control for a grid-connected dc-ac power converter, termed hybrid angle control (HAC) that combines the dc-based matching control with a novel nonlinear angle feedback reminiscent of (though not identical to) classic droop control. The synthesis of HAC is inspired by the complementary benefits of the dc-based matching and ac-based grid-forming controls as well as ideas from direct angle control and nonlinear damping assignment. The proposed HAC is applied to a nonlinear converter model that is connected to an infinite bus or a center-of-inertia dynamic grid models. We provide parametric sufficient existence, uniqueness, stability, and boundedness conditions that are met by appropriate choice of control parameters. Next, we take into account the safety constraints of power converter, and synthesize a new current-limiting control that is compatible with HAC. Last, we present details on the practical implementation of HAC that are followed by a robustness analysis (which showcases a theory-practice gap), uncover the intrinsic droop behavior of the HAC, derive a feedforward-like ac voltage and power control, and illustrate the behavior of the closed-loop system with simulation case studies.