AIM-Toolbox: Automated Impedance Measurement Toolbox for Screening Stability Risks


The Automated Impedance Measurement (AIM)-toolbox is the world’s first impedance measurement software that is used in several commercial projects of High-Voltage Direct-Current (HVDC) transmission systems. The AIM-toolbox enables to automatically measure impedance profiles of power electronic systems across a wide frequency range. The measured impedances can be used to screen the risks of sub-synchronous resonances and harmonic instabilities in power-electronic-based power systems (PEPS), e.g., wind farms, photovoltaic (PV) power plants, multi-terminal HVDC (MTDC) systems, and energy islands, etc.    

Over the past decade, Prof. Xiongfei Wang and his eGRID group members have been persistently in developing methods and tools for screening stability risks in power-electronic-based power systems (PEPS). The highly nonlinear and time-varying dynamics of power electronic converters significantly complicate the stability analysis of power systems. After years of efforts, eGRID researchers have developed rigorous theories and methods for black-box modeling and dynamics analysis of PEPS [1]-[5], from which, the AIM-Toolbox is developed mainly by Prof. Xiongfei Wang and Assist. Prof. Heng Wu.

Value Proposition  

The recent years have witnessed massive integration of power electronic converters in modern power and energy systems, e.g., renewable power generation, electrification of transportation and various industry sectors. The power-electronic-based sources and loads tend to interact with one another, fundamentally changing the dynamics of power systems. Power outages resulted from system interactions of power converters are increasingly reported across the globe, raising significant concerns from system operators. Therefore, prescreening stability risks are mandatory for system operators to permit new grid connections of power converters. Manufacturers of power converters also need to assure that their converter products meet the dynamic specifications of system operators. However, with the proliferation of power electronic converters, the brute-force numerical simulation studies become cumbersome and computationally challenging, and it often fails to shed any insight into the causes of instabilities.

To tackle the challenge, the AIM-toolbox is developed to map the small-signal dynamics of PEPS into frequency domain, and thus a computationally-efficient stability analysis can be performed by using frequency-domain analysis tools. Further, with the rigorous theoretical basis laid by eGRID researchers, the AIM-toolbox ensures accurate impedance measurement and reliable stability prediction.

Technology Competence

In recent years, there have been increasing R&D efforts on the impedance measurement of power electronic systems. Compared to other impedance measurement tools, the unique feature of AIM-toolbox is that the impedance matrix of PEPS can be directly obtained in the stationary reference frame without involving any transformations. Further, the AIM-Toolbox is fully compatible with the electromagnetic simulation environment, and the measurement process is fully automated. A user-friendly interface is provided, and users can flexibly specify the frequency resolution and frequency range for the impedance measurement. With a single-click on the run button, the needed impedance data for system stability analysis is generated.

Use Cases in Practice

The AIM-toolbox has been commercially licensed to two European Transmission System Operators (TSOs), i.e., Energinet (Danish TSO) and TenneT GmbH (German TSO), and successfully used in several commercial HVDC projects [6]. Together with TenneT GmbH, the AIM-toolbox has also been further developed for stability analysis of multi-vendor MTDC power systems [7], [8], see Fig. 1.

Fig. 1.  AIM-toolbox is adopted for stability assessment of multi-vendor MTDC power systems with TenneT TSO GmbH.

Besides the industry applications, the AIM-toolbox has also been licensed to Yonsei University, South Korea, for research and education purposes. A free-demo version of AIM-toolbox is available to check its functions and features, and it has been shared with 3 more German TSOs (50Hertz, Amprion, Transnet BW), Elia Group (Belgian TSO), the National HVDC Centre, UK, Dominion Energy (American power and energy company), AusNet services (Australian energy company) and NR Electric. Please do not hesitate to contact us if you are interested.  



Xiongfei Wang


Heng Wu




X. Wang, L. Harnefors, and F. Blaabjerg, “Unified impedance model of grid-connected voltage-source converters,” IEEE Trans. Power Electron., no. 2, pp.1775-1787, 2018.
Y. Liao and X. Wang, “Impedance-based stability analysis for interconnected converter systems with open-loop RHP Poles” IEEE Trans. Power Electron., no. 4, pp. 4388-4397, 2020.
Y. Liao and X. Wang, “Stationary-frame complex-valued frequency-domain modeling of three-phase power converters,” IEEE Jour. Emer. Sel. Top. Power Electron., no. 2, pp. 1922-1933, 2020.
H. Wu and X. Wang, “Dynamic impact of zero-sequence circulating current on modular multilevel converters: complex-valued ac impedance modeling and analysis,” IEEE Jour. Emer. Sel. Top. Power Electron., no. 2, pp. 1947-1963, 2020.
Y. Liao and X. Wang, “Small-signal modeling of ac power electronic systems: critical review and unified modeling,” IEEE Open Jour. Power Electron., vol. 2, pp. 424-439, 2021.
D. Yang, X. Wang, M. Ndreko, W. Winter, R. Juhlin and A. Krontiris. “Automation of impedance measurement for harmonic stability assessment of MMC HVDC systems,” Proc. 18th Wind Integr. Work., 2019.
H. Wu, X. Wang, Y. Liao, M. Ndreko, R. Dimitrovski and W. Winter, “Development of an AC/DC impedance matrix measurement Toolbox for MTDC System” in 20th Proc. Wind Integr. Workshop, 2021.
Y. Liao, H. Wu, X. Wang, M. Ndreko, R. Dimitrovski, and W. Winter, “Stability and sensitivity analysis of multi-vendor, multi-terminal HVDC systems,” arXiv preprint arXiv:2111.12013 (2021).