Power grid dynamics and stability with a high penetration of renewable energies

The urgent need to decrease CO2 emissions to mitigate the severe damag- ing effects of climate change is accelerating the transition towards renewable en- ergy sources across all sectors. In particular, variable renewable energy sources (VRES), such as wind and solar, will be key to achieve decarbonization. This will fundamentally change traditional energy practices and it presents significant difficulties that must be addressed.

In the energy sector, the integration of large shares of VRES poses two main challenges. On one hand, stable grid operation is based on the continuous balance between generation and demand, which must be met in real-time. Traditionally, this is achieved using controllable energy sources, such as fossil fuels. However, VRES are highly unpredictable and intermittent. On the other hand, unlike VRES, which are integrated into the grid through power electronics, conventional power plants provide inertia and control frequency dynamics. Hence, the progressive replacement of conventional generation by VRES requires novel grid operation strategies.

This thesis explores the path towards achieving a fully renewable power grid, with a particular focus on the frequency dynamics and stability issues that may arise in highly renewable scenarios. Using different regions as case studies, we investigate common challenges such as the impact of reduced inertia, higher con- trol requirements, and transmission line overloads.

Our approach is to represent high-voltage power grids as networks of inter- acting conventional power plants or substations connected via power transmission lines. We describe bus dynamics with different models based on the swing equation. By using realistic grid representations and validating the models with actual data whenever possible, our results are not merely theoretical speculation and offer useful insights.

Initially, we analyze different islands, including Gran Canaria and the Balearic Islands in Spain, as well as Gokçeada in Turkey. Islands are pivotal in the energy transition due to their relatively small size and typically abundant renewable sources. In the context of renewable-dominated scenarios, we estimate control requirements and potential infrastructure upgrades to enhance grid resilience. Additionally, we discuss the role of high-voltage direct current (HVDC) technology and batteries in providing frequency control. Subsequently, we extend our study to the Continental European grid, illustrating the challenges of operating a larger interconnected system. In this case, we examine the propagation of distur- bances and inter-area oscillations, as well as grid stability in general.

Overall, this thesis contributes to the ongoing research efforts concerning the large deployment of renewable energies worldwide. It provides different methodologies for analyzing power grid dynamics and stability within scenarios characterized by a large penetration of renewables.