Comparing solutions to strengthen inertia in the Belgian power system: Impacts on frequency stability and grid integration

Details

Supervisors

De Jaeger, Emmanuel

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

enThe Belgian power system is transitioning rapidly towards renewable energy sources, leading to reduction in synchronous inertia. As conventional thermal and nuclear generation is gradually displaced by converter-interfaced wind and solar (i.e., connected to the grid through power electronics rather than directly rotating machinery), the system becomes more vulnerable to fast frequency deviations following generation losses. This raises concerns about frequency security, particularly during periods when nuclear units are offline. This thesis investigates the frequency stability of the Belgian high-voltage transmission grid under low-inertia conditions, using root-mean-square simulations in DIgSILENT PowerFactory. A simplified eight-bus model of the Belgian grid is developed, including synchronous generators with governors and excitation systems, converter-interfaced generation, interconnections with neighbouring countries and frequency-dependent loads. Two operating scenarios are considered: a winter peak and a basic case, each tested with and without nuclear generation and across three levels of renewable energy sources penetration. The results show that the Belgian grid remains frequency-secure in all tested cases when nuclear is online. In the basic case without nuclear, the frequency nadir falls below 49 Hz following the reference disturbance. This would trigger automatic load shedding in real operation. Three mitigation techniques are then evaluated: synchronous condensers, grid-forming converters and fast frequency response from battery storage. Two synchronous condensers planned by Elia are found to improve the frequency response but only when equipped with a flywheel does the nadir cross back above 49 Hz. Connecting the future offshore capacity through grid-forming control produces a substantial recovery, restoring the nadir and the rate of change of frequency to levels comparable to the nuclear reference. Activating fast frequency response on batteries also restores the frequency nadir, though without the RoCoF benefit that grid-forming provides. These findings suggest that the converter control strategy for Princess Elisabeth Island is a consequential planning choice for Belgian frequency security in a no-nuclear period and that combining the three mitigation techniques yields the best overall frequency performance.