Registration Link: https://ieee.webex.com/weblink/register/r6963988008874291b3cfae9c199a7552

Abstract

The increasing integration of renewable energy sources, interfaced with the grid via power converters, has introduced significant small-signal stability challenges. Globally, power systems with high penetration of power electronics have experienced oscillations across a wide frequency spectrum, often triggered by minor changes in operating conditions, control parameters, or load. As penetration rates approach 100% in parts of modern grids, these dynamic interactions pose a critical threat to reliable operation, underscoring the urgent need for effective diagnostic tools.

Impedance-based stability analysis has emerged as a flexible and practical method due to its black-box characteristics, allowing engineers to assess stability margins through direct measurements of currents and voltages via frequency scanning, and guide the stability-oriented design of power electronics.

This tutorial will present the fundamentals of impedance-based analysis, illustrate its application with a detailed example to solidify understanding, and review recent advances in impedance models for MIMO systems, influence of controller’s reference frame orientation, and symmetricity of the impedance matrix.  It will conclude with a discussion of current challenges and future research directions in this vital field.

Tutorial Objectives

This tutorial is designed for a broad audience, including undergraduate and postgraduate students, PhD researchers, and industry professionals in power systems and power electronics.

The primary objectives are:

• To introduce participants to the fundamentals of impedance-based stability analysis.
• To build confidence and capability in participants for implementing various impedance approaches and using available tools to model and assess the stability condition and margin of realistic systems.
• To Illustrate the core principles through a practical, step-by-step example of impedance evaluation and stability assessment using MATLAB/Simulink.
• To provide exposure to practical problems and their solutions through case studies that represent real-world scenarios.
• To enhance the participants’ ability to critically assess the appropriate tools for a given scenario, model the system, and evaluate stability in practical engineering problems.

By the end of this tutorial, attendees will gain a solid conceptual foundation, a clear understanding of the methodology’s practical application, and an awareness of the state-of-the-art and open problems in impedance-based stability analysis.

Outline

1. AC impedance models and basics of impedance-based analysis (Duration: 40 minutes)

• A historical perspective on the Impedance-Based Stability Analysis methodology
• Dq-domain impedance models (Belkhayat, 1997)
• Original Sequence-domain impedance (Jian Sun, 2011)
• Modified Sequence-domain impedance (our work, 2016)

1. Stability Assessment Techniques for Impedance Networks (Duration: 40 minutes)

• PE Impedance Network Modelling (Chen et al, 2019) https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8705360
  • Impedance rotation & aggregation (Rygg et al., 2017)
  • Weakest point identification (Chen et al., 2019)
• Stability Oriented Network Planning (Firdaus et al., 2020)

5-minute break

• Application Examples (Duration: 30 minutes)
• DFIG based wind turbines
• SSO in MMC-HVDC linked with wind farms
  • Impedance re-shaping
• Synchronization stability
• Stability of Black-Box systems
  • Impedance re-shaping

5-minute break

1. Impedance estimation case study with simulation example (Duration: 40 minutes)

• Grid connected converter example definition
• Small signal model of the VSC in Matlab
• From voltage and current measurement to impedance in Matlab
• Analysis and discussion of simulation results

1. Recent Advances in the Impedance-based Method (Duration: 40 minutes)

• Revisiting Impedance-based Analysis
• Frequency Coupling Across Various Reference Frames
• Evaluation of Coupling Strength and Coupling Factor and Corrective Factor
• Influence of different controllers and reference-frame Angle in dq-frame
• Implications for Stability Analysis
• Single coordinate Bode Plot analysis for MIMO systems
• Stability margin evaluation in new method

1. Questions & Wrap-up (Duration: 20 minutes)

Learning outcomes

After completion of the tutorials, participants will gain a good understanding of:

• The small signal stability challenges in converter-dominated grids.
• The different Impedance models in different domains to assess the most appropriate for a given scenario.
• How to implement a basic assessment of the impedance-based stability analysis principles in Matlab.
• Techniques for implementing the methodology in a network of power VSCs
• The new advances in the impedance method for complex MIMO systems, applications and current limitations

About the Instructor

Dr Marta Molinas

Professor, Norwegian University of Science and Technology, Norway

IEEE Fellow

Dr. Marta Molinas is currently a Professor in the Department of Engineering Cybernetics at the Norwegian University of Science and Technology (NTNU) in Trondheim, Norway. She received her M.E. degree from Ryukyu University, Nishihara, Japan, in 1997, and her Doctor of Engineering degree from the Tokyo Institute of Technology, Tokyo, Japan, in 2000.

Dr. Molinas was a Guest Researcher at the University of Padova, Italy, in 1998. From 2004 to 2007, she held a postdoctoral research position at NTNU, and from 2008 to 2014, she served as a Professor in the Department of Electric Power Engineering at the same institution. In 2014, she was a Visiting Scholar at Columbia University’s Earth Institute. She was also an invited fellow in Japan under the JSPS Invitational Fellowship in both 2008 and 2022. Her research interests include the stability of power electronic systems, harmonics, instantaneous frequency, and nonstationary signals from both human and machine sources. Prof. Molinas is an Editor for the IEEE Journal of Emerging and Selected Topics in Power Electronics (JESTPE), the IEEE Journal of Emerging and Selected Topics in Industrial Electronics (JESTIE), and Scientific Reports (Nature Publishing Group). She also serves as an Advisor to the Board of IEEE Electrification Magazine and as an Associate Editor for the IEEE Transactions on Power Electronics. She is a member of the Administrative Committee (AdCom) of the IEEE Transportation Electrification Council and previously served on the AdCom of the IEEE Power Electronics Society from 2009 to 2011. In 2016, Dr. Molinas was General Chair of IEEE COMPEL 2016, and Program Chair of IEEE PowerTech 2011. She is a Fellow of the IEEE.