Investigating the Converter-Driven Stability of an Offshore HVDC System

Matthias Quester, Fisnik Loku, Otmane El Azzati, Leonel Noris, Yongtao Yang and Albert Moser
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Matthias Quester: Institute of High Voltage Equipment and Grids, Digitalization and Energy Economics, RWTH Aachen University, Templergraben 55, 52062 Aachen, Germany
Fisnik Loku: Institute of High Voltage Equipment and Grids, Digitalization and Energy Economics, RWTH Aachen University, Templergraben 55, 52062 Aachen, Germany
Otmane El Azzati: Institute of High Voltage Equipment and Grids, Digitalization and Energy Economics, RWTH Aachen University, Templergraben 55, 52062 Aachen, Germany
Leonel Noris: DNV, Arnhem Utrechtseweg 310, 6812 AR Arnhem, The Netherlands
Yongtao Yang: DNV, Arnhem Utrechtseweg 310, 6812 AR Arnhem, The Netherlands
Albert Moser: Institute of High Voltage Equipment and Grids, Digitalization and Energy Economics, RWTH Aachen University, Templergraben 55, 52062 Aachen, Germany

Energies, 2021, vol. 14, issue 8, 1-27

Abstract: Offshore wind farms are increasingly built in the North Sea and the number of HVDC systems transmitting the wind power to shore increases as well. To connect offshore wind farms to adjacent AC transmission systems, onshore and offshore modular multilevel converters transform the transmitted power from AC to DC and vice versa. Additionally, modern wind farms mainly use wind turbines connected to the offshore point of common coupling via voltage source converters. However, converters and their control systems can cause unwanted interactions, referred to as converter-driven stability problems. The resulting instabilities can be predicted by applying an impedance-based analysis in the frequency domain. Considering that the converter models and system data are often confidential and cannot be exchanged in real systems, this paper proposes an enhanced impedance measurement method suitable for black-box applications to investigate the interactions. A frequency response analysis identifies coupling currents depending on the control system. The currents are subsequently added to the impedance models to achieve higher accuracy. The proposed method is applied to assess an offshore HVDC system’s converter-driven stability, using impedance measurements of laboratory converters and a wind turbine converter controller replica. The results show that the onshore modular multilevel converter interacts with AC grids of moderate short-circuit ratios. However, no interactions are identified between the offshore converter and the connected wind farm.

Keywords: converter-driven stability; HVDC; offshore; MMC; converter; replica; impedance-based stability analysis; interactions (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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