Revisiting Grid-Forming and Grid-Following Inverters: A Duality Theory

Power electronic converters for integrating renewable energy resources into power systems can be divided grid-forming and grid-following inverters. They possess certain similarities, but several important differences, which means that the relationship between them is quite subtle sometimes obscure. In this article, a new perspective based on duality proposed to create insights. It successfully unifies grid interfacing synchronization characteristics of two inverter types in symmetric, elegant, technology-neutral form. Analysis shows inverters are xmlns:xlink="http://www.w3.org/1999/xlink">duals each other ways including a) controllers: frequency droop control phase-locked loop (PLL); b) grid-interfacing characteristics: current-following voltage-forming voltage-following current-forming; c) swing current-angle voltage-angle swing; d) inner-loop output impedance shaping admittance shaping; e) strength compatibility: strong-grid instability weak-grid instability. The equations also derived dual form, reveal dynamic interaction strength, controllers, controllers. Insights generated cases poor stability both small-signal transient/large-signal. theoretical analysis simulation results used illustrate single-inverter systems, two-inverter multi-inverter networks.