Stability of a system with high penetration of power electronic converters: impact of wind events and transmission outages

Abstract

Nowadays, renewable energy sources take a larger share in energy production. The power systems encounter a significant turn because of the growth of renewable energy sources, which brings more power electronics into the grid. For instance, modern wind farms are equipped with full converter wind turbines to ensure a higher energy yield. Furthermore, HVDC links, equipped with power electronic converters, have become popular because of their controllability and are installed in various power systems. The power electronic converters replace the synchronous machines, and instabilities at higher frequencies may now occur. It thus has led to a reshape in the classification of power system stability. Wind turbines are placed where the wind potential is the highest. They are grouped in wind parks which concentrate a large amount of active power production. Variations in wind speeds thus lead to rapid changes in the loading of the system, which may jeopardize its stability.

This thesis aims at assessing the stability of a system mainly composed of power electronic converters. A fictitious network is tested under various scenarios, and solutions are proposed to ensure a secure system for the different tests realized. The simulation tool used applies the phasor approximation method, therefore, the fast interactions that may occur between the converters and the network are not analyzed here.

The thesis is divided into five parts. The first part introduces the stability issues encountered in a power system mainly composed of power electronics. It also describes the classification of wind events and their intensity. The second part illustrates the network studied and the modeling of the converters. It highlights their different control modes. The third part focuses on wind events and their impact on the stability of the system. The evolution of the voltages is studied for two different wind events: the Ramping event and the Storm event. Those events are combined with operations on HVDC links. Their active power productions are changed according to the rules of the energy market. Solutions are proposed to mitigate the impact of those events on the network voltages. The fourth part focuses on transmission outages. Solutions are proposed to ensure a secure system after the incident occurred. Finally, the last part describes the necessity of having grid forming converters in the system. It shows the evolution of voltage phasors for the system with and without a grid forming converter. Finally, an overall conclusion is drawn.