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Ideally-Smooth Transition between Grid-Forming and Grid-Following Inverters based on State Mapping Method

Zhenshuai Liu, Yitong Li, Zirui Wang, Jiashuo Gu, Yao Qin, Jinjun Liu

Abstract

There has been widespread global increasing use of renewable energy sources, which are usually connected to the electricity grids via power electronic inverters. Traditionally, these inverter-based resources operate in either grid-forming (GFM) or grid-following (GFL) mode. But more recently, the need of switching between these two modes are glowingly required because of the complex operation scenarios of systems such as source-side limitations, grid-side services, fault disturbances, etc. However, due to the differences between GFM and GFL modes, a direct switching between them would lead to large oscillations or even instability of inverters. Therefore, in this paper, a method called state mapping method for analyzing the switching transient and designing the switching control is proposed. Based on this method, an ideally-smooth transition between GFM and GFL can be achieved. The effectiveness of the proposed method is verified by both the theoretical analysis and experiment tests.

Ideally-Smooth Transition between Grid-Forming and Grid-Following Inverters based on State Mapping Method

Abstract

There has been widespread global increasing use of renewable energy sources, which are usually connected to the electricity grids via power electronic inverters. Traditionally, these inverter-based resources operate in either grid-forming (GFM) or grid-following (GFL) mode. But more recently, the need of switching between these two modes are glowingly required because of the complex operation scenarios of systems such as source-side limitations, grid-side services, fault disturbances, etc. However, due to the differences between GFM and GFL modes, a direct switching between them would lead to large oscillations or even instability of inverters. Therefore, in this paper, a method called state mapping method for analyzing the switching transient and designing the switching control is proposed. Based on this method, an ideally-smooth transition between GFM and GFL can be achieved. The effectiveness of the proposed method is verified by both the theoretical analysis and experiment tests.

Paper Structure

This paper contains 13 sections, 8 equations, 24 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Analysis of Mode Transition Transients
  3. State Space Modeling
  4. Modeling Mode Transition
  5. State Mapping Method
  6. Control Design for Smooth Mode Transition
  7. Synchronization Control
  8. Amplitude Control
  9. Experimental Results
  10. Case 1: Experiments from Grid-Following to Grid-Forming
  11. Case 2: Experiments from Grid-Forming to Grid-Following
  12. Case 3: Experiments on Different Operating Points
  13. Conclusions

Figures (24)

  • Figure 1: Modeling of GFL and GFM used for studying smooth transition.
  • Figure 2: Unified State Space Representations for GFL and GFM.
  • Figure 3: Derivation of the Equilibrium Points and the Domain of Attraction for GFL and GFM.
  • Figure 4: The Essence of Mode Transitions.
  • Figure 5: Comparison of Whether to Apply State Mapping Method.
  • ...and 19 more figures