Grid Capacity - Challenges and Opportunities

Electric power grids have a limited capacity for safe and reliable transfer of power. Due to the ongoing large-scale expansion of variable renewable energy sources, such as wind and solar, there is a growing need for rapid grid
capacity increase.

This thesis explores methods for improving and expanding grid capacity through control of converter-interfaced energy resources, including wind and solar plants, and battery energy storage systems. The objective is to safely operate existing networks at their capacity limits, which improves grid utilisation and reduces reliance on slow infrastructure upgrades. Specifically, voltage and power flow constraints in distribution networks, and power flow limits in transmission networks are considered in the presented research.

If the ongoing energy transition in Sweden and Europe is to continue at the necessary pace to achieve ambitious climate goals, a large number of renewable energy sources must be quickly connected to the electricity grid. The expansion of this type of electricity generation is limited by a lack of grid capacity in the high-voltage transmission network and by bottlenecks in the distribution networks, which supply electricity to end customers, such as households and industries. To ensure sufficient grid capacity in the long term, the grid
companies reinforce and expand the existing network infrastructure by constructing new lines and transformers. However, this process is often both costly and slow.

This thesis deals with alternative ”non-wire” solutions to grid reinforcement, which allow the expansion rate of renewable energy sources to be increased with minimal need for infrastructure upgrades. To achieve this, control features already built into the power electronic converters that connect wind and solar power plants to the grid are utilised. Through control algorithms developed within the research project, the flexibility of these grid resources can be utilised to adapt production to respect the grid’s current (or power) and voltage limits. If other flexible grid resources, such as energy storage systems, are available, they
can also be used to optimise the grid capacity usage. By controlling the charging and discharging of energy storage systems in different parts of the grid, virtual power lines can be created, and the total grid capacity can be increased without the need for new lines.