Grid Forming: Academic Approaches and Modelling Aspects

LUNCH

Lecture 1 (45 min.)
Grid-forming and wide-area damping control
Rossano Musca (University of Palermo, Italy)

Grid-forming converters represent a unique opportunity in contributing to power system operation and control. A relevant area which recently started to receive attention is the application of grid-forming converters within the wide-area damping control of power systems. Thanks to the flexibility in the formulation of the power-angle control law, grid-forming technology can play a fundamental role in the actuation of wide-area damping control schemes. The tutorial will first recall the main concepts and characteristics of wide-area damping control. Then, the tutorial will delve into the integration of grid-forming converters within specific architectures for the wide-area damping control of power systems. It will be shown the potential benefit in terms of damping of inter-area oscillations and improvement of power system dynamics, highlighting the theoretical aspects and referring to the interconnected power system of Continental Europe as demonstrative example.

Discussion (15 min)

Lecture 2 (45 min.)
Grid-Forming by Wind and PV Power Plants:
Control Interaction between Primary Converter and Grid-side Converter
Horst Schulte (HTW Berlin, Germany)

In this tutorial, analytical models of four-degree-of-freedom wind turbines and two-stage photovoltaic generators are derived to investigate the influence of grid-forming control on the wind turbine’s mechanical loading as well as on the power electronic and passive components of the photovoltaic system.

The analytical models are further utilized to design the necessary extensions of primary converter controllers to enable grid-forming operation. Particular attention is given to the requirements and control engineering realization for power tracking to enable the provision of fast frequency reserves by wind and photovoltaic
power plants.

Discussion  (15 min)

Coffee Break

Lecture 3 (45 min.)
Current limitation techniques for grid-forming converters
Frédéric Colas (University of Lille, France)

Grid-forming converters, unlike synchronous machines, are highly sensitive to overcurrents and therefore require dedicated protection mechanisms. This tutorial first introduces two classical strategies for current limitation. The first is the increase of virtual impedance, which effectively reduces the current but can introduce long transients. The second is the saturation of current references, which directly enforces a current limit but may compromise the ability of the system to resynchronize after a fault. Simulation results will demonstrate that while both methods are capable of protecting the converter, they can have adverse consequences for stability after large disturbances.

The second part of the tutorial focuses on large disturbance stability. Building on static models originally developed for synchronous machines, the presentation shows how grid-forming converters react under severe events such as bolted faults, and sudden phase shifts. Traditional stability assessment tools such as the Equal Area Criterion are shown to be of limited use for converters due to their inherent damping. Fault scenarios highlight the difficulty of maintaining synchronism once current limitation is activated. Classical enhancement methods such as phase angle freezing and voltage-dependent adaptations—based on adaptive inertia or power reference reduction—are discussed. These methods can improve stability during voltage dips but fail to address pure phase-shift disturbances, leaving a gap in robustness.

The third part introduces a novel approach based on the concept of virtual power. By redefining the power variable used in control, this method decouples current limitation from large disturbance stability and increases the stability margin of the system. It allows converters to resynchronize reliably after severe faults, whether caused by voltage dips or angle shifts. Experimental results obtained on a 7.5 kVA test bench confirm the validity of the method and its potential for practical deployment.

Discussion (15 min)

Lecture 4 (45 min.)
Frequency Characteristics and Requirements for Grid-forming Converter Control
Massimo Bongiorno (Chalmers University of Technology, Sweden)

Grid Forming (GFM) capabilities are today considered an essential requirement for grid-connected converters, especially for high-voltage/high-power applications. Particularly in the last decade, the trend for massive integration of renewable energy sources and the need for increased controllability of the electric-power systems, has led to a shift in the way how converters are controlled, from fast-acting controllers to a more intrinsic converter’s reaction to grid disturbances. At the same time, an univocally accepted definition of GFM control still does not exist. Starting from the needs of the connecting grid, the aim of this talk is to discuss the requirements of GFM converters and to investigate the needed frequency characteristics that this kind of systems must offer towards the grid. Aiming for continuous grid support, modifications in the classical control structure for GFM that allow to naturally provide vital services such as inertial support, damping in the sub-synchronous frequency range and sink for unbalances and harmonics, will be exploited.

Discussion & Closing (15 min)