Tutorials

Tutorial Title:

Immittances of Converters in Power Systems: Theory, Modeling and Applications

Instructors Team:

Dr. Jian Sun, Professor, Rensselaer Polytechnic Institute

Abstract:

Immittance, which combines the term impedance and admittance and may refer to either one, is arguably the most important attribute of any electrical component in power systems. Most power system studies require immittance models in one form or another. The development of immittance models for generators, transformers and transmission lines form the core of power engineering education, and parameters needed for such models are readily available from manufacturers or even public sources. Immittance is also the basis for specifying products used in different system designs, including transmission and distribution networks, protection, voltage regulation, and harmonic mitigation.

The situation was very different when it came to immittance of converters in power systems. For a long time there was no consideration of immittance at all for wind turbines, PV inverters and other types of the so-called converter-based resources. An underlying fundamental difficulty is that immittance cannot be directly calculated for grid-connected converters because of their nonlinear and time-periodic behavior. Research to address this challenge has been going for about 20 years but didn’t attract much practical interest at the beginning. The situation has changed in recent years because of the need for practical methods to study the stability of renewable energy and HVDC systems. Immittance-based frequency-domain methods fulfilled this need and provided a general framework for stability analysis and design of future converter-based grids.

Tutorial Outline:

This tutorial presents an introduction to the theory and applications of immittance-based frequency-domain modeling and analysis methods for converters in power systems. The tutorial covers the following topics:

1.            Basic Concepts and Applications: We start by discussing the importance of immittance in power systems and the difficulty to define it for converters. After a brief review of different definitions attempted in the early days of research, the concept of small-signal sequence immittance is introduced. Practical methods to determine frequency responses of small-signal sequence immittances by laboratory measurement and numerical simulation are then presented. The lecture concludes with the formulation of an immittance-based converter-grid system model for frequency-domain stability analysis based on the classical Nyquist stability criterion.

2.            Immittance Models and Characteristics: Analytical methods to develop immittance models for PV inverters, wind turbines, as well as different HVDC converters are reviewed. The mathematical principle and process are explained in sufficient detail to allow those interested in analytical work to apply the methods. The rest of this part focuses on practical use of analytical models to understand the effects of converter design on immittance response and system stability. For this purpose, the overall frequency spectrum is divided into low and high frequency ranges. The effects of different control functions in each frequency range are explained to provide insights into their design tradeoffs.

3.            System Models and Stability Analysis: Stability of individual wind and PV inverters/farms connected to the grid can be studied by using a system model that resembles a single-input-single-output (SISO) feedback loop. For more complex systems, a multiple-input-multiple-output (MIMO) formulation is introduced. Both grid-following and grid-forming controls are considered. Frequency-domain stability analysis of MIMO systems based on the generalized Nyquist criterion is explained. Practical applications of the MIMO formulation includes power systems with multiple renewable power plants in different locations, multi-terminal HVDC, as well as future hybrid ac-dc grids.

Instructor Biography:

Dr. Jian Sun received his B.S. degree in electrical engineering from the Nanjing University of Aeronautics and Astronautics, China, in 1984, his M.S. degree in electrical engineering from the Beijing University of Aeronautics and Astronautics in 1989, and his Ph.D. degree in electrical engineering from the University of Paderborn, Germany, in 1995. He is a professor in the Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute (RPI), Troy, New York. He is also the director of the New York State Center for Future Energy Systems, RPI.

 

 

Tutorial Title:

Grid-Forming Converters: Principles and Practices

Instructors Team:

Prof. Xiongfei Wang, KTH Royal Institute of Technology, Sweden

Prof. Heng Wu, Aalborg University, Denmark

Prof. Fangzhou Zhao, Aalborg University, Denmark

Dr. Bo Fa, Aalborg University, Denmark

Abstract:

The grid-forming (GFM) technology is emerging as a promising approach for the massive integration of inverter-based resources (IBRs) into electrical grids. Being controlled as a voltage source behind an impedance, GFM-IBRs can provide adequate services to enhance the reliability and resilience of the power network, and they also feature higher stability robustness against grid strength variations than conventional IBRs. In recent years, there is a growing consensus on the need for GFM-IBRs in future power-electronic dominated power systems. Many research and development (R&D) efforts have been initiated, by governments, power system operators, energy developers, and vendors of IBRS, on the technical specifications/grid codes, hardware, and control solutions for GFM-IBRs.

This tutorial intends to cover both the basics and advances in GFM-IBRs that can fit the requirements of the evolving technical specifications/grid codes. The tutorial will start with the basic principles and technical specifications of GFM-IBRs, which will be followed by the small-signal modeling and stability analysis of GFM-IBRs under various conditions. Then, the dynamics analysis of GFM-IBRs under large grid disturbances, e.g., grid faults and phase jumps, will be performed, covering the transient stability analysis and current limitation strategies. In the end, perspectives on the prospects and challenges with the grid integration of GFM-IBRs will be shared.

Tutorial Outline:

  1. Basic of GFM-IBRs and technical specifications (Xiongfei Wang: 40 min)
  2. Small-signal stability and control of GFM-IBRs (Fangzhou Zhao and Heng Wu: 60 min)
    1. Small-signal dynamics and control interaction analysis (Fangzhou Zhao)
    2. Small-signal dynamics under the current limitation mode (Heng Wu)
  3. Large-signal stability and control of GFM-IBRs under grid faults (Bo Fan and Heng Wu: 30 min)
    1. Transient stability analysis of GFM-IBRs without current limitation triggered (Heng Wu)
    2. Current-limiting control of GFM-IBRs and its transient stability impact (Bo Fan)
  4. Prospects and Challenges with GFM-IBRS (Xiongfei Wang: 20 min)

Instructor Biography:

Xiongfei Wang is a Professor at KTH Royal Institute of Technology, Sweden, and a part-time Professor with AAU Energy, Aalborg University, Denmark. He has been an active tutorial instructor (e.g., PEDG, APEC, ECCE, EPE, eGrid) on the stability and control of inverter-based resources and power systems. Dr. Wang is an IEEE Fellow and the recipient of the Richard M. Bass Outstanding Young Power Electronics Engineer Award, the IEEE PELS Sustainable Energy Systems Technical Achievement Award, the Isao Takahashi Power Electronics Award, and the Clarivate Highly Cited Researcher during 2019-2021. (Email: xiongfei∂kth.se)

Heng Wu is currently an Assistant Professor with AAU Energy, Aalborg University, Denmark. His research interests include the modeling and stability analysis of power-electronic-based power systems. He is a member of the GB grid forming best practice expert group formed by national grid ESO, UK, and the subgroup leader of Cigre working group B4/C4.93 “Development of grid forming converters for secure and reliable operation of future electricity systems”. He is identified as the world’s top 2% scientist by Stanford University in 2019. (Email: hew∂energy.aau.dk)

Bo Fan is currently a Postdoctoral Researcher with AAU Energy, Aalborg University, Aalborg, Denmark. His research interests include power system stability, power electronics, smart grid, distributed control, and nonlinear systems. He was the recipient of the Best Reviewer Award of IEEE Trans. Smart Grid in 2019, the Outstanding Reviewer Awards of IEEE Trans. Power Syst. in 2019 and 2021, the Chinese Association of Automation (CAA) Excellent Doctoral Dissertation Award in 2020, and the Marie Skłodowska-Curie Individual Fellowship in 2021. (Email: bof∂energy.aau.dk)

Fangzhou Zhao is currently an Assistant Professor with AAU Energy, Aalborg University, Denmark. His research interests include modeling, analysis and control of grid-following/grid-forming converters, modular multilevel converters, and grid emulation systems. He serves as a guest Associate Editor for the IEEE Journal of Emerging and Selected Topics in Power Electronics. (Email: fzha∂energy.aau.dk).

 

 

Tutorial Title

Power Hardware-in-the-Loop (PHIL) – Real-time simulation and closed loop stability

Instructors Team:

Sebastian Hubschneider

OPAL-RT Germany GmbH

E: sebastian hubschneider ∂does-not-exist.opal-rt com

Abstract

Power Hardware-in-the-Loop (PHIL) test beds offer a comprehensive platform for conducting in-depth, safe, repeatable, and realistic testing of future electrical systems, equipment, and devices. This includes facilitating rapid prototyping of controllers and hardware as well as obtaining regulatory approval. However, the successful design and operation of a PHIL system requires meticulous system layout and necessitates making compromises. These compromises extend beyond the limitations of technical equipment and require careful consideration of the conflicting requirements of PHIL systems. Specifically, this includes balancing the need for high bandwidth and dynamics, as well as low step size and high stability.

In this tutorial, Sebastian Hubschneider (OPAL-RT TECHNOLOGIES) will introduce the PHIL method and categorize its requirements. The tutorial will cover essential considerations for constructing a closed-loop system, followed by the challenges involved in building a robust PHIL system.

The tutorial will consist of both theoretical and practical sessions. During the practical session, participants will learn how to stabilize real-time simulations and achieve closed-loop operation in PHIL setups. An overview of the real-time simulation software package, HYPERSIM, will be provided, and participants will have the opportunity for hands-on practice on their own laptop. The practical exercises will include editing a basic network and a PHIL emulation, designed to gain insight into the challenges associated with setting up test environments. Participants will adjust models to explore potential solutions and identify their limitations. Practical advice will be offered, and questions related to PHIL stability will be addressed.

Tutorial Outline

Presentation on the PHIL method, necessary considerations and solutions (approx. 40 min)

Introduction to real-time simulation software HYPERSIM and monitoring tool ScopeView (approx. 30 min)

Hands-on on participants laptops (110 min)

-              Real-time simulation and numerical instability

-              Closed-loop stability of PHIL experiments

Instructor Biography

Sebastian Hubschneider completed his studies in electrical engineering and information technology at the Karlsruhe Institute of Technology (KIT) in June 2015. Following his master's degree, he worked as a research associate at the Institute of Electric Energy Systems and High-Voltage Technology at KIT. In 2022, he successfully defended his PhD thesis on Power Hardware-in-the-Loop systems and their application in distribution system testing.
Since April 2022, Sebastian has been working as an R&D Engineer and PHIL specialist at the German subsidiary of OPAL-RT TECHNOLOGIES. In this role, he focuses on digital twins, real-time simulation, power grid simulation, Power Hardware-in-the-Loop, closed-loop stability, and various research projects in these fields.

Tutorial Title

Introduction to Virtual synchronous machines – inverters for a stable and well-damped grid

Instructors Team:

Fabio Mandrile (FM), Politecnico di Torino, fabio mandrile ∂does-not-exist.polito it

Florian Reissner (FR), Tel Aviv University, reissner ∂does-not-exist.tauex tau ac il

George Weiss (GW), Tel Aviv University, gweiss ∂does-not-exist.tauex tau ac il

Abstract

The current shift from fossil-based energy production towards renewable power in the electric grid is radically challenging the power grid. A promising solution to this challenge is the Virtual Synchronous Machine (VSM): inverters behaving like synchronous generators to provide grid services and grid support. Therefore, the VSM-controlled inverters can contribute to system inertia, damping and the decentralized regulation of voltage and frequency. Moreover, their very fast response time, and their ease of reprogramming to add new features in their control algorithm, opens ways to improve their performance beyond what is possible with synchronous generators.

     This tutorial will start presenting requirements for safe grid operation and stability requirements that impose bounds on damping and inertia from the power electronics perspective. Then, the concept of VSM will be presented and its advantages compared to other control strategies are highlighted.

     We analyze the performance of a microgrid comprising VSMs in island mode as well as when connected to a main grid. We also consider microgrids comprising both VSM and synchronous machines and show the interdependence between system parameters, VSM parameters and the physical equipment of the inverter. Finally, we introduce more advanced concepts for the safe and stable operation of VSMs: the influence of measurement errors and grid voltage distortions, black start mechanisms and ways to improve the damping of oscillations and fault ride-through using communication links between inverters.

Tutorial Outline

  • Introduction to power electronics for the grid
    • Key applications, subsystems, structures
    • Examples of issues (faults) encountered
  • VSM concept and modeling
    • Introduction to VSMs
    • VSM Functionalities (generation and load, fast charging)
    • Comparison of VSM models proposed in literature
    • Experimental examples
  • Enhancing grid stability and damping using VSM
    • Robustness with respect to faults, region of attraction.
    • Robustness with respect to measurement errors and harmonics
    • Techniques for damping oscillations
    • Experimental results

Lecture Target and Basic Requirements (Briefly describe what is the targeted audience for this tutorial (PhD students, professionals, industry). Note any equipment or space beyond a laptop and projector that shall be required for your tutorial in order to be effective. Also list the targeted audience and tutorial difficulty level, including any pre-requisite knowledge.)

Instructor Biography

Fabio Mandrile received the M.Sc. and Ph.D. degrees in electrical engineering from Politecnico di Torino, Italy, in 2017 and 2021, respectively. He is currently assistant professor at Dipartimento Energia G. Ferraris at Politecnico di Torino. His main research interests are virtual synchronous machines and power electronics for grid-connected applications, on which he focused his Ph.D. and current research activity.

Florian Reissner received the B.Sc. and M.Sc. degrees from the Technical University of Berlin, Germany, in 2015. He is currently pursuing the Ph.D. degree with the Power Electronics for Renewable Energy Group, Tel Aviv University. From 2015 to 2020, he worked in project management with Vinci Energies, Lyon, and he was an Innovation Consultant and design thinking coach with incubators in Frankfurt and Berlin. In 2020, he started working as an Early Stage Researcher (funded by the European Commission) at Tel Aviv University. His current research interests include control techniques in power systems and control theory.

George Weiss received the M.Eng. degree in control engineering from the Polytechnic Institute of Bucharest, Romania, in 1981, and the Ph.D. degree in applied mathematics from Weizmann Institute, Rehovot, Israel, in 1989. He was with Brown University, Providence, RI, USA; Virginia Tech, Blacksburg, VA, USA; Ben-Gurion University, Be’er Sheva, Israel; the University of Exeter, U.K.; and Imperial College London, U.K. He is leading research projects of the European Commission, the Israeli Ministry of Energy and the Israeli Electricity Company. His research interests include distributed parameter systems, operator semigroups, passive and conservative systems, power electronics, repetitive control, sampled data systems, and wind-driven power generators. He teaches courses from the general area of control theory, functional analysis and power electronics, and has given tutorials and plenary lectures at several conferences.

Tutorial Title:

Power System Dynamic Modelling, Performance Assessment, Needs and Services Identification, and Grid Connection Process with a High Share of Inverter-based Resources

Instructors Team:

Dr. Babak Badrzadeh, Technical Director, Power Systems, Aurecon

Abstract:

Power systems around the world are experiencing a significant uptake of inverter-based resources (IBR) coincident with a reduction in the number of online synchronous generators. IBRs and synchronous generators have fundamentally different dynamic performance characteristics resulting in a difference in the overall power system dynamic performance. These differences will become more prevalent as IBR uptake increases in the power system. Reductions in system strength, inertia, damping of small-signal oscillations, fault levels, and other synchronous characteristics are the results of the transition from power systems with the dominance of synchronous generators to those with very few synchronous generators online.

These changes in system characteristics have caused new and emerging power system phenomena, in particular the risk of adverse interactions among the control systems of multiple nearby IBRs. Such phenomena either did not previously exist or when they did, they were much easier to identify and address, e.g., sub-synchronous control interactions between IBRs and series compensated lines. Changes in the power system and generation mix have meant that these phenomena are likely to occur more often (as experienced in other countries), will have the potential to impact a larger part of the power system, and their impact will be greater than it used to be. This could potentially result in major supply disruptions if such phenomena are not understood and addressed pre-emptively. A testament to this widespread impact is the growing need for IBR remediations in real generator connection applications including the need for installation of devices such as synchronous condensers or control system tuning to avoid instabilities.

Phasor-domain transient (PDT) simulation tools also commonly known as root mean-square (RMS) simulation have been used for several decades for bulk power system dynamic modelling and performance assessment. However, worldwide experiences indicate that these tools have often not been able to predict phenomena associated with IBR control system response which is due to the simplifications inherent in these tools. Detailed wide-area modelling, using electromagnetic transient (EMT) tools and representing explicitly most parts of the power system with dynamic models, has therefore been increasingly used in recent times in particular in countries/regions with higher IBR penetration to address the problems discussed above.

Tutorial Outline:

This tutorial presents power system dynamic modelling, performance assessment, needs and services identification, and grid connection process with a high share of IBR. The tutorial covers the following topics:

1. Modelling and analysis: The presentation first compares PDT and EMT modelling with regard to factors such as the level of modelling details included, the accuracy achieved, and examples where PDT is not suitable for power system planning and operation, as well as those where PDT is sufficiently accurate. Both the grid-following and grid-forming inverters are investigated. Various screening methods are discussed for making a decision on the necessity of wide-area EMT modelling for each specific scenario, or limiting the number of EMT studies in situations where several tens or hundreds of EMT studies may be required. The presentation then provides guidance on the principles of network equivalencing for instances where a large part but not the whole power system is represented in EMT. Lastly, the advantages and disadvantages of offline EMT simulation, co-simulation, and real-time EMT simulation are elaborated on.

2. Attributes and system services: The increased uptake of grid-forming IBRs and the flexibility to provide multiple grid-support capabilities will mean that the overall power system and individual generator performance technical requirements are becoming increasingly intertwined. A comparative assessment of the capabilities, limitations and services possible with each of the grid-following and grid-forming inverters is discussed and compared against those traditionally provided by synchronous generators.

3. Grid connection process: Increased need for EMT modelling is prompting a change in the grid connection processes adopted by network owners and system operators worldwide. More systematic processes for model acceptance testing, conformity assessment (including tuning), and model validation are discussed for IBR interconnection studies focusing on areas with high concentration of several sizeable IBRs, whether grid-forming or grid-following.

Instructor Biography:

Dr. Badrzadeh is Technical Director – Power Systems with Aurecon Group. Prior to joining Aurecon he spent the career at Mott MacDonald Transmission and Distribution (UK), Vestas Wind Systems (Denmark), and the past nine years with Australian Energy Market Operator as the Manager of Operational Analysis and Engineering team.
He is a recognised worldwide expert in the areas of power system modelling and analysis, impacts of grid-connected and distributed inverter-based resources from operational, connections and planning perspectives, and power system restoration. This is backed by strong knowledge of legal and regulatory frameworks in Australian power system having led many rule changes and guidelines development.
Throughout my career he has been involved in more than 300 power system modelling and analysis works in four continents including design, grid integration, planning and operational impact assessments, and generator connections, commissioning and model validation projects. In particular, he has played a key role in the worldwide establishment of wide-area electromagnetic transient (EMT) modelling, and the overarching area of system strength.
He has been privileged to lead some of the most interesting and challenging tasks including South Australian black system event analysis, development of NEM power system EMT model, and ongoing management of NEM system security with increased uptake of inverter-based resources including the development of necessary technical requirements and guidelines.
He is currently the Convener of CIGRE Working Groups B4.83, C2.26 and C4.56, a member of CIGRE SC C2 Strategic Advisory Committee, and until February 2021 long-time Convener of Australian Power System Modelling Reference Group (PSMRG) and System Restart Working Group (SRWG).
He was the main organiser of Australian system strength workshop held on 6 November 2020 which attracted more than 1300 registrations. He served as keynote and invited speaker in several international events, and chaired multiple conference sessions, and a recipient of 2019 ESIG Engineering excellence award.