Full Program

The lecture begins from the basics of the grid-forming control and presents a didactic approach to design the closed loop system which simultaneously controls the active power and synchronizes the converter. A coherent method is proposed to analyse whether the grid-forming scheme embeds a current loop or not. Different variants of control are given depending on the requirements about inertial effect or primary frequency support. The grid forming control system is tested in stationary, transient and islanding conditions. The virtual power method is shown to be able to retain stability, especially in case of a phase shift. The lecture covers various converter types, beginning with an ideal voltage-source converter (VSC) modelled as a simple voltage source, followed by modular multilevel converters (MMCs) and VSCs with LC filters. The theoretical approach is illustrated with experimental results. Finally, the lecture provides a comparison between grid-following and grid-forming controllers for grid-connected converters.

The lecture introduces the concept of Harmonic Stability Assessment (HSA) of power systems with a high share of CIDERs. To this end, the lecture introduces the concept of Harmonic State-Space (HSS) model of a generic power system formulated by combining the HSS models of the resources and the grid in closedloop configuration. The HSS model of the resources is obtained from the Linear Time-Periodic (LTP) models of the CIDER components transformed to frequency domain using Fourier theory and Toeplitz matrices as this approach is capable of representing the coupling between harmonic frequencies in detail. The system matrix of the HSS models on powersystem or resource level is employed for eigenvalue analysis in the context of HSA. A sensitivity analysis of the eigenvalue loci w.r.t. changes in model parameters, and a classification of eigenvalues into control-design variant, control-design invariant, and design invariant eigenvalues is given together with some application examples.

The lecture focuses on the synchronization of converters to the power system, presenting different synchronization methods and discussing their influence on the stability and harmonic distortion in Converter-Interfaced Distributed Energy Resources (CIDERs). The cross-coupling phenomena among the synchronization and other control loops are conceptually explained, and their significant influence on converter stability is demonstrated. Nonlinear modelling techniques to analyse CIDER stability and behaviour under harmonic distorted conditions are presented and applied to different grid scenarios. Particular attention is given to the case where detailed models of CIDERs are unavailable to system operators due to Intellectual Property (IP) protection by power electronics manufacturers. For this scenario, grey-box models of CIDERs utilizing structured uncertainties are derived, and robust stability tools are used to guarantee interoperability among converters from different vendors.

The lecture first introduces the concept of complex frequency, which extends the conventional instantaneous frequency of a signal. Then the lecture defines the concepts of “local synchronization” and “transient slack capability” The latter definition is based on a port-Hamiltonian modelling approach and discusses energy and control requirements of inverter-based generation to stand large disturbances. Three model-based necessary conditions are proposed to represent the minimum requirements for a device to synchronize to the grid and behave as an energy slack during a transient. A variety of examples based on conventional synchronous and induction machines as well as grid following (GFL) and grid forming (GFM) controllers are utilised to illustrate, both analytically and through simulations, illustrate the concepts of local synchronization and transient slack capability. The last example presents a “dual-GFM” controller, which illustrates how to leverage the proposed framework to design novel control schemes that go beyond conventional GFL and GFM architectures.

As power system dynamics are increasingly dominated by comparatively many CIDERs, detailed systemlevel stability studies have become a central part in stability assessment, but remain difficult due to limitations in today’s simulation tools and the complexity of assembling credible models. Building on experience modelling parts of the Danish and Australian power systems, this talk focuses on the practical workflow and decision making required to conduct large-scale time-domain studies: obtaining and parameterizing models, combining different model types, handling missing data, and navigating the computational limits of EMT, RMS, and hybrid simulators. Motivated by these real-world challenges, the session further discusses the use of a range of dynamic model-reduction approaches, including classical, data-driven, and ML-based methods. The talk concludes with open research questions and emerging needs for future grids targeting high or fully non-synchronous operation.

Gustavo Valverde, Anibal Sanjab, Florin Capitanescu, Christian Rehtanz, Gianluigi Migliavacca, Zhengshuo Li, Innocent Kamwa

Mathaios Panteli, Rodrigo Moreno, Dimitris Trakas, Magnus Jamieson, Charalambos Konstantinou, Pierluigi Mancarella, Goran Strbac, Nikos Hatziargyriou