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Control of AC-AC interlinking converters for multi-grids

Jeremy Watson, Ioannis Lestas

TL;DR

This work tackles stability and power sharing in networks of microgrids interconnected by AC-AC ILCs. It introduces a passivity-based framework that yields decentralized stability criteria, accommodating both grid-following and grid-forming ILCs, and proposes a partially grid-forming controller that blends GFL and GFM behavior to strengthen weaker sub-grids. Through a combination of theoretical analysis and simulations, the paper demonstrates that sharing DC regulation across ILCs and employing GFM on at least one side enhances damping and inertia provisioning, improving stability in multi-grid configurations. The approach is validated on case studies, including a two-MG network and the IEEE 39-bus system, highlighting practical relevance for scalable stabilization of future multi-grid networks with AC-AC interlinks.

Abstract

This paper considers the control of AC-AC inter-linking converters (ILCs) in a multi-grid network. We overview the control schemes in the literature and propose a passivity framework for the stabilization of multi-grid networks, considering both AC grid-following and AC grid-forming behavior for the ILC connections. We then analyze a range of AC/AC interlinking converter control methods derived from the literature and propose suitable controllers for this purpose including both AC grid-forming and grid-following behavior. The controller we propose is partially grid-forming; in particular, it is based on a combination of a grid-following and a grid-forming converter to improve the stability properties of the network. Simulation results and theoretical analysis confirm that the proposed ILC control designs are appropriate for the multi-grid network.

Control of AC-AC interlinking converters for multi-grids

TL;DR

This work tackles stability and power sharing in networks of microgrids interconnected by AC-AC ILCs. It introduces a passivity-based framework that yields decentralized stability criteria, accommodating both grid-following and grid-forming ILCs, and proposes a partially grid-forming controller that blends GFL and GFM behavior to strengthen weaker sub-grids. Through a combination of theoretical analysis and simulations, the paper demonstrates that sharing DC regulation across ILCs and employing GFM on at least one side enhances damping and inertia provisioning, improving stability in multi-grid configurations. The approach is validated on case studies, including a two-MG network and the IEEE 39-bus system, highlighting practical relevance for scalable stabilization of future multi-grid networks with AC-AC interlinks.

Abstract

This paper considers the control of AC-AC inter-linking converters (ILCs) in a multi-grid network. We overview the control schemes in the literature and propose a passivity framework for the stabilization of multi-grid networks, considering both AC grid-following and AC grid-forming behavior for the ILC connections. We then analyze a range of AC/AC interlinking converter control methods derived from the literature and propose suitable controllers for this purpose including both AC grid-forming and grid-following behavior. The controller we propose is partially grid-forming; in particular, it is based on a combination of a grid-following and a grid-forming converter to improve the stability properties of the network. Simulation results and theoretical analysis confirm that the proposed ILC control designs are appropriate for the multi-grid network.
Paper Structure (32 sections, 1 theorem, 24 equations, 11 figures, 4 tables)

This paper contains 32 sections, 1 theorem, 24 equations, 11 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Background and literature review
  3. Preliminaries and notation
  4. Passivity conditions for multi-grids
  5. Passivity and related definitions
  6. Microgrid dynamics
  7. ILC dynamics
  8. Passivity conditions for AC-AC ILCs
  9. General passivity conditions for ILCs
  10. Control design for AC-AC ILCs
  11. Control objectives
  12. ILC models
  13. Grid-following ILC model
  14. Grid-forming ILC model
  15. Partially grid-forming ILC model
  16. ...and 17 more sections

Key Result

Theorem 1

Suppose there exists an equilibrium $x^\ast = [x^\ast_1, x^\ast_2, ... x^\ast_{|N|}, z^\ast_1, z^\ast_2, ... z^\ast_{|Z|}]^T$ for the interconnected MG and ILC dynamics, for which Assumptions mgpass and ilcpass are satisfied. Then, such an equilibrium point is locally asymptotically stable.

Figures (11)

  • Figure 1: ILC notation.
  • Figure 2: Network diagram.
  • Figure 3: Representation of a network containing three AC MGs and two ILCs.
  • Figure 4: Representation of a general network with multiple MGs and ILCs, where each MG has a single connection point between it and the ILC(s).
  • Figure 5: Representation of a larger network with multiple MGs and ILCs, where any MG may have multiple connection points to various ILCs.
  • ...and 6 more figures

Theorems & Definitions (9)

  • Definition 1: Passivity khalil1991TPS_paper
  • Remark 1
  • Remark 2
  • Remark 3
  • Remark 4
  • Theorem 1
  • Definition 2: Equilibrium-state observability
  • Remark 5
  • Definition 3: Input observability boukhobza2007