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Deliverables Technology

PROMOTioN WP16 – Successful commissioning and testing of a multi-terminal HVDC demonstrator

Within PROMOTioN, a unique laboratory-scale multi-terminal HVDC demonstrator – the MMC Testbench – was built at RWTH Aachen University. The system commenced operation in April 2019. First tests have demonstrated a good match between full-scale HVDC network simulations and the MMC Testbench.

Due to its high level of adaptability, the laboratory can serve a wide range of study purposes, from the demonstration of operational strategies for HVDC grids to the analysis of harmonic interaction of HVDC and wind turbine converters.

 

MMC

The future integration of multi-terminal HVDC networks into the European power grids presents novel challenges to transmission grid operators, grid planners and manufacturers. A major obstacle to building HVDC networks is the limited experience available regarding their operation as well as their interaction with AC transmission systems and offshore wind power plants.

Within PROMOTioN, a laboratory-scale multi-terminal HVDC demonstrator – the MMC Testbench – has been built at RWTH Aachen University. The system has commenced operation in April 2019 and now serves to address these issues. At the heart of this testbench are eight laboratory-scaled Modular Multilevel Converters (MMCs) manufactured by OPAL-RT, which can be configured as half- and full-bridge converters. The scaled MMCs contain 10 cells per arm, have a rated DC voltage of 400 V and a power rating of 6 kW. The DC network is represented by cascaded Pi sections, which can be configured as symmetrical monopole and bipole. To investigate the interactions between HVDC grids, offshore wind power plants and AC transmission systems, the MMCs are embedded in a real-time simulation of the surrounding AC systems by employing four-quadrant linear power amplifiers. First tests have displayed a good match between EMT simulations of a full-scale HVDC network and the MMC Testbench.

Due to its high level of adaptability, the laboratory allows for a broad range of investigations. Some key aspects of the research and the demonstrations to be carried out within the PROMOTioN project are:

  • Demonstrations regarding the controllability of different HVDC network configurations and operational strategies.
  • Studies of the interaction between offshore wind parks, HVDC grids and their converters as well as AC transmission systems. This includes the demonstration of frequency support strategies and the operation of the offshore wind parks in grid forming control mode.
  • Analysis of the frequency dependent impedance of MMCs and wind turbine converters and the harmonic stability in offshore AC collector networks in different operation modes.

More details regarding test cases planned in PROMOTioN are provided in deliverable 16.1 on this website.

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