Revisiting grid-forming and grid-following inverters: a duality theory
File(s)
Accepted version
Author(s)
Li, Yitong
Gu, Yunjie
Green, Timothy
Type
Journal Article
Abstract
Power electronic converters for integrating renewable energy resources into power systems can be divided into grid-forming and grid-following inverters. They possess certain similarities, but several important differences, which means that the relationship between them is quite subtle and sometimes obscure. In this article, a new perspective based on duality is proposed to create new insights. It successfully unifies the grid interfacing and synchronization characteristics of the two inverter types in a symmetric, elegant, and technology-neutral form. Analysis shows that the grid-forming and grid-following inverters are duals of each other in several ways including a) synchronization controllers: frequency droop control and phase-locked loop (PLL); b) grid-interfacing characteristics: current-following voltage-forming and voltage-following current-forming; c) swing characteristics: current-angle swing and voltage-angle swing; d) inner-loop controllers: output impedance shaping and output admittance shaping; and e) grid strength compatibility: strong-grid instability and weak-grid instability. The swing equations are also derived in dual form, which reveal the dynamic interaction between the grid strength, the synchronization controllers, and the inner-loop controllers. Insights are generated into cases of poor stability in both small-signal and transient/large-signal. The theoretical analysis and simulation results are used to illustrate cases for single-inverter systems, two-inverter systems, and multi-inverter networks.
Date Issued
2022-11-01
Date Acceptance
2022-02-12
Citation
IEEE Transactions on Power Systems, 2022, 37 (6), pp.4541-4554
ISSN
0885-8950
Publisher
Institute of Electrical and Electronics Engineers
Start Page
4541
End Page
4554
Journal / Book Title
IEEE Transactions on Power Systems
Volume
37
Issue
6
Copyright Statement
© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Sponsor
Engineering & Physical Science Research Council (E
Engineering & Physical Science Research Council (EPSRC)
Identifier
https://ieeexplore.ieee.org/document/9714816
Grant Number
EP/S000909/1
EP/T021780/1
Subjects
Science & Technology
Technology
Engineering, Electrical & Electronic
Engineering
Inverters
Phase locked loops
Synchronization
Voltage control
Frequency control
Power system stability
Power system dynamics
Duality
synchronization
frequency droop control
phase-locked loop (PLL)
grid-forming inverter (GFM)
grid-following inverter (GFL)
grid strength
SYNCHRONIZATION
CONVERTERS
STABILITY
SYSTEMS
Energy
0906 Electrical and Electronic Engineering
Publication Status
Published
Date Publish Online
2022-02-16