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Impedance characterization of wind turbine converters using PHiL & CHiL

Power system stability depends more and more on grid-connected power converters. Especially in converter-dominated and purely converter-based grids, such as offshore collector grids evacuating wind energy via HVDC systems, dynamic interactions over a wide frequency range may cause resonances and subsequent system outages.

To de-risk the development of future converter-dominated grids, it is essential to analyze the system stability over a wide frequency range. A common method to study the stability of power systems with a high converter penetration level is the impedance-based stability criterion, which requires input-impedance models of the relevant converter. Hence, it is prudent to derive accurate impedance models of given power converters and validate them against their physical counterparts.

 

Within the frame of the PROMOTioN project, DNV GL has conducted the world’s first MW-level wind turbine power converter input-impedance measurement carried out in an independent testing lab. A measurement setup based on harmonic current perturbation has been prototyped in the Flex Power Grid Lab (FPGL) of DNV GL to measure the input-impedance a commercial 1 MW wind turbine converter from Ming Yang Smart Energy, Zhongshan, China. The measurements are used to verify analytically derived impedance models and compared with the input-impedance measurements of a control replica of the wind turbine converter. The results show decent agreement between the power converter and its control replica for frequencies up to 1.5 kHz.
The impedance measurement set-up of the FPGL was presented to a broad audience of stakeholders on 15th August 2019 in Arnhem, Netherlands.


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