Grid-forming WT control strategies for OWPPs connected to HVDC via diode rectifiers




Central and West Zealand

This project will study and compare two different control strategies for 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 technology 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 corresponding 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 and compare two different strategies for controlling such grid-forming type-4 WPPs/WTs. Some of the corresponding tasks include:

  • Reviewing the relevant literature related to OWPPs connected to HVDC via DRs.
  • Modelling the studied system in a dynamic simulation tool e.g., Simulink.
  • Implementing the two different control strategies for the model.
  • Comparing the performance and robustness of the control strategies for different operating conditions, system parameters and disturbances.
L. Yu, R. Li and L. Xu, "Distributed PLL-based Control of Offshore Wind Turbine Connected with Diode-Rectifier based HVDC Systems", IEEE Transactions on Power Delivery, Advance online publication.


Sound background in wind turbine/plant control; Knowledge of electrical power systems and control engineering; Command of Simulink Power Systems or similar; Good English speaking and writing skills

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