Small-signal modelling and stability analysis of OWPPs connected to HVDC via diode rectifiers




Midt- og Vestsjælland

This project will study the small-signal stability characteristics of offshore wind power plants connected to HVDC via diode rectifiers.
Network infrastructure connecting offshore wind power plants (offshore WPPs, OWPPs) with onshore grids is needed to fully exploit Europe’s offshore wind resources. High-voltage direct current (HVDC) is seen as the main technology as distance from shore increases, but the high cost of power converter tech-nology is, among others, hindering the deployment of such networks. In quest of lowering the costs of offshore wind energy, new control strategies taking advantage of the type-4 (full-converter) wind turbines’ (WTs’) own power converters have been recently shown to enable the use of diode rectifiers (DRs), instead of voltage source converters (VSCs), for connecting OWPPs to HVDC networks.

Until now, HVDC-connected OWPPs have relied on the HVDC offshore voltage source converters (VSCs) to form the offshore AC grids i.e., control their voltage magnitude and frequency. This has enabled the use of WT and WPP control schemes similar to those utilised onshore. DRs offer reduced costs and increased reliability, but they lack the control capabilities of VSCs, and their use relies on delegating the correspond-ing control functions to the WT front-end VSCs. This requires fundamentally different WT and WPP control schemes, changing their control philosophy from grid-following units to grid-forming units. This project will study the small-signal stability characteristics of such an offshore AC grid based on several aggregated grid-forming type-4 WPPs/WTs. Some of the corresponding tasks include:

  • Reviewing the relevant literature related to OWPPs connected to HVDC via DRs.
  • Developing/deriving nonlinear state-space models analytically/symbolically for the corresponding subsystems.
  • Deriving the corresponding small-signal models by linearising the state-space models analytically/symbolically.
  • Validating the models by means of dynamic simulations e.g., in Simulink.
  • Studying the small-signal stability characteristics of the studied system through eigenvalue/modal analysis of the validated small-signal models.
S. I. Bernal-Pérez, S. C. Añó-Villalba, and R. M. Blasco-Giménez, “Stability Analysis of HVDC-Diode Rectifier Connected Off-shore Wind Power Plants”, in Proceedings of the IEEE Industrial Electronics Society 41st Annual Conference (IECON 2015), Yokohama, Japan, 9th–12th Nov. 2015, pp. 4040–4045.


Sound mathematical background; Knowledge of electrical power systems and control engineering; Programming skills in MATLAB or similar; Good English speaking and writing skills

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