Modeling and enhancing transient stability of grid-forming converters
Author(s)
Arjomandi Nezhad, Ali
Type
Thesis
Abstract
Grid-forming (GFM) Inverter-based resources (IBRs) are suggested to be deployed in power grids as a response to the emerging needs in IBR-dominant power systems. Their software-defined dynamic characteristics are constrained by several limitations, such as the limitations in electric current output. GFM IBRs might enter the current-saturation operation mode facing a severe disturbance. Operating in the current-saturation operation mode causes a distinct behaviour from their normal operation mode. This thesis aims at modelling and enhancing the transient stability of GFM IBRs considering the current saturation.
In the modelling phase, the conditions for transitioning between the normal and current-saturation operation modes are identified. Based on these conditions, the large-signal model for the transient stability of GFM IBRs is developed. It is observed that the angle of the saturated current plays a prominent role in shaping the post-disturbance dynamics of GFM IBRs. Then, the circumstances under which the GFM IBR converges to the saturated stable equilibrium point (satSEP), which is an emerging challenge due to the current saturation, are explored. It is also demonstrated that the current saturation causes a decrease in the post-fault deceleration area of the equal area criterion.
In the enhancing phase, two main challenges, which are mentioned in the modelling phase, are compensated: (1) The possibility of convergence to the satSEP is mitigated by tuning the angle of the saturated current to satisfy the sufficient condition for avoiding the convergence, (2) The decreased post-fault deceleration is compensated by adding two corrective signals to the active power controller (APC). These corrective signals are evaluated through a model predictive control (MPC), which aims to minimize the deviations of the APC angle from the stable equilibrium point, subject to a safe post-fault trajectory. The modelling and enhancement measures are verified by several electromagnetic transients (EMT) simulation case studies in Simulink/MATLAB environments.
In the modelling phase, the conditions for transitioning between the normal and current-saturation operation modes are identified. Based on these conditions, the large-signal model for the transient stability of GFM IBRs is developed. It is observed that the angle of the saturated current plays a prominent role in shaping the post-disturbance dynamics of GFM IBRs. Then, the circumstances under which the GFM IBR converges to the saturated stable equilibrium point (satSEP), which is an emerging challenge due to the current saturation, are explored. It is also demonstrated that the current saturation causes a decrease in the post-fault deceleration area of the equal area criterion.
In the enhancing phase, two main challenges, which are mentioned in the modelling phase, are compensated: (1) The possibility of convergence to the satSEP is mitigated by tuning the angle of the saturated current to satisfy the sufficient condition for avoiding the convergence, (2) The decreased post-fault deceleration is compensated by adding two corrective signals to the active power controller (APC). These corrective signals are evaluated through a model predictive control (MPC), which aims to minimize the deviations of the APC angle from the stable equilibrium point, subject to a safe post-fault trajectory. The modelling and enhancement measures are verified by several electromagnetic transients (EMT) simulation case studies in Simulink/MATLAB environments.
Version
Open Access
Date Issued
2024-11-01
Date Awarded
2025-06-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Pal, Bikash
Sponsor
European Union
Grant Number
956433
Publisher Department
Department of Electrical and Electronic Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)