Impedance-based stability and sensitivity analysis of multi-terminal MMC-HVDC systems

Impedance-based stability and sensitivity analysis of multi-terminal MMC-HVDC systems

A. Prof. Heng Wu, Aalborg University

Prof. Xiongfei Wang, Aalborg University



The multi-terminal HVDC (MTDC) system based on modular multilevel converters (MMCs) is increasingly developed in the high-voltage transmission grid. The MTDC could introduce various benefits to the power system by bringing in more operational flexibility. Yet, the fast control implemented in MMC stations might interact with AC/DC grid, leading to system oscillations in a wide frequency range. On the other hand, the control details of each vendor-specific MMC are not available to the transmission system operator (TSO) due to the intellectual property (IP) concern. Hence, small-signal stability studies of the MTDC system represented by black-box models are urgently needed.

This tutorial intends to share our experience gained from a collaborative research project with German TSO TenneT, which focuses on the small-signal stability and sensitivity analysis of the MTDC system. Among other stability assessment methodologies, impedance-based stability analysis is adopted to facilitate TSOs dealing with black-box models. This tutorial will start with introducing a systematic impedance modeling methodology that is capable of capturing the frequency coupling dynamics of the MMC system. Then, a developed PSCAD-compatible software toolbox that enables the accurate AC/DC impedance (matrix) measurement of the MMC will be introduced, together with sharing our experience of some practical considerations for the impedance measurement. Next, stability studies will be performed based on impedance measurement data, first for a single MMC station connecting to the AC grid, then extended to the MTDC system. In the end, the proposed multi-level sensitivity analysis approach will be introduced, with which, root causes of the unstable operation of the MTDC system can be identified simply based on the impedance measurement data, which does not require the knowledge of the detailed control scheme used in each MMC station.



Heng Wu is currently an Assistant Professor with AAU Energy, Aalborg University, Denmark. His research interests include the modelling and stability analysis of the power electronic based power systems. He is the main participant of the research project collaborating with TenneT TSO that focuses on the stability analysis of multi-terminal MMC-HVDC systems.From 2015 to 2017, He was an Electrical Engineer with NR Electric Co., Ltd, Nanjing, China. He was a guest researcher with Ørsted Wind Power, Fredericia, Denmark, in 2018, and Bundeswehr University Munich, Germany, in 2019. He was a Postdoctoral researcher with Aalborg University, Aalborg, Denmark, from 2020 to 2021. He is the Co-Chair of IEEE Task Force on Frequency-domain Modeling and Dynamic Analysis of HVDC and FACTS, the member of the technical committee (TC) of European Academy of Wind Energy (EAWE), the member of GB grid forming best practice expert group formed by national grid ESO, UK, the member of Cigre working group B4.85 and B4/C4.93, and the Steering Committee Member of Cigre next generation network (NGN), Denmark. His research interests include the modelling and stability analysis of the power electronic based power systems. He is identified as world’s top 2% scientist by Stanford University from 2019. He received the 2019 Outstanding Reviewer Award of the IEEE TRANSACTIONS ON POWER ELECTRONICS and the 2021 Star Reviewer Award of the IEEE JOURNAL of EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS.


Xiongfei Wang is a Full Professor and Leader of Research Group on Electronic Power Grid (eGRID) at the Department of Energy, Aalborg University, Aalborg, Denmark, as well as a part-time Full Professor at KTH Royal Institute of Technology, Stockholm, Sweden. His research interests include modeling and control of grid-interactive converters, stability and power quality of power-electronic-based power systems. In these areas he has led 15+ industry projects since 2016, ranging from solar inverters and wind farms to STATCOM and HVDC systems. He has also been an active tutorial instructor at IEEE conferences (e.g. PEDG, APEC, ECCE, EPE, eGrid). He serves as the Co-Editor-in-Chief for the IEEE Transactions on Power Electronics, and as the Associate Editor for the IEEE Journal of Emerging and Selected Topics in Power Electronics. He has received 7 IEEE Prize Paper Awards, the 2018 Richard M. Bass Outstanding Young Power Electronics Engineer Award, the 2019 IEEE PELS Sustainable Energy Systems Technical Achievement Award, and the Highly Cited Researcher in the Web of Science during 2019-2021. 

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