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Oscillations between Grid-Forming Converters in Weakly Connected Offshore WPPs

Sulav Ghimire, Kanakesh V. Kkuni, Gabriel M. G. Guerreiro, Emerson D. Guest, Kim H. Jensen, Guangya Yang

Abstract

This paper studies control interactions between grid-forming (GFM) converters exhibited by power and frequency oscillations in a weakly connected offshore wind power plant (WPP). Two GFM controls are considered, namely virtual synchronous machine (VSM) and virtual admittance (VAdm) based GFM. The GFM control methods are implemented in wind turbine generators (WTGs) of a verified aggregated model of a WPP and the control interaction between these GFM WTGs is studied for several cases: cases with the same GFM control methods, and cases with different GFM control methods. A sensitivity analysis is performed for the observed oscillations to understand which system parameter affects the oscillations the most. Several solution methods are proposed and the inapplicability of some of the conventional solution methods are elaborated in this paper.

Oscillations between Grid-Forming Converters in Weakly Connected Offshore WPPs

Abstract

This paper studies control interactions between grid-forming (GFM) converters exhibited by power and frequency oscillations in a weakly connected offshore wind power plant (WPP). Two GFM controls are considered, namely virtual synchronous machine (VSM) and virtual admittance (VAdm) based GFM. The GFM control methods are implemented in wind turbine generators (WTGs) of a verified aggregated model of a WPP and the control interaction between these GFM WTGs is studied for several cases: cases with the same GFM control methods, and cases with different GFM control methods. A sensitivity analysis is performed for the observed oscillations to understand which system parameter affects the oscillations the most. Several solution methods are proposed and the inapplicability of some of the conventional solution methods are elaborated in this paper.
Paper Structure (11 sections, 3 equations, 8 figures)

This paper contains 11 sections, 3 equations, 8 figures.

Table of Contents

  1. Introduction
  2. System Description and Modelling
  3. WTGs with same GFM controls
  4. WTGs with same GFM controls and same control tunings
  5. WPP with same GFM control and different inertia constant
  6. WTGs with different GFM controls
  7. Oscillation FFT during steady state and transients
  8. Sensitivity of oscillations to electrical proximity between converters
  9. Sensitivity of oscillations to grid SCR
  10. Potential Solution Methods
  11. Conclusion

Figures (8)

  • Figure 1: Network layout for GFM control interaction studies.
  • Figure 2: Control diagrams for VSM-based and VAdm-based GFM controllers employed in the WTGs. Source: ghimire2023gridforming.
  • Figure 3: Control oscillations in a system with same GFMs. A SCR change from 3.2 to 1.6 is applied at $t=1\ s.$
  • Figure 4: Oscillations between VSM and VSM0H controls following a grid SCR change from 3.2 to 1.6.
  • Figure 5: Fourier transform of the selected oscillation signals for two cycles after the SCR change event.
  • ...and 3 more figures